On 25 January, when mining company Rio Tinto reported that one of their Caesium-137 radioactive capsules had gone missing, Western Australian authorities faced a seemingly impossible task.

They had to locate a pea-sized capsule anywhere along a 1,400km (870 mile) route stretching from the Gudai-Darri mine in the north of the state to a depot just north of Perth’s city centre.

Authorities sprung into action, mobilising specialist search crews to look for the capsule, with firefighters among those asked to foray from their usual summer tasks.

Experts were called in from across the country: nuclear science specialists, the emergency management agency and radiation protection officials.

Authorities believed the capsule had fallen off a radiation gauge that was being transported from a Rio Tinto mine site on 12 January to a storage facility in the north-eastern suburbs of Perth.

They thought vibrations during transit may have caused the bolts to become loose, allowing the capsule to fall through gaps in the casing and truck.

Caesium-137 (Cs-137) capsules are commonly used in radiation gauges in mining to measure the density of certain materials. But if you come into contact with one, it can cause severe burns and expose you to the equivalent of 10 x-rays per hour.

Before notifying the public to the threat, on 26 January, authorities began searching in Perth and around the mine site in Newman.

On 27 January, an urgent health warning was issued to notify the public about the risk posed by the radioactive capsule. Health authorities had a simple message to anyone who may come across it: Stay away.

“It emits both beta rays and gamma rays so if you have it close to you, you could either end up with skin damage including skin burns,” the state’s Chief Health Officer Andy Robertson warned.

Authorities were concerned it may have become lodged in the tyre of a passing car.

By 27 January, search parties were in full force looking for the tiny capsule. But they were not scouting for it using their eyes – they were using portable radiation survey meters.

The survey meters are designed to detect radioactivity within a 20m radius.

“We are not trying to find the small capsule by eyesight. The radiation equipment will hopefully lead us to it,” a police spokesperson said the following day.

Police focused their efforts on the GPS route the truck had taken, and on sites close to Perth’s metropolitan and high-density areas.

One site along the Great Northern Highway was prioritised by police on 28 January after unusual activity on a Geiger counter – a device used for measuring radioactivity – was reported by a member of public.

But that search did not uncover the capsule.

The next day, additional resources requested from Australia’s federal government had been approved and those overseeing the search began planning its next phase.

With the new equipment in Western Australia and ready for use by 30 January, the search ramped up.

An incident controller at the state’s emergency services department, Darryl Ray, described the new tools provided by the government only as “specialised radiation detection equipment”.

Local media reported that radiation portal monitors and a gamma-ray spectrometer were among the new items being used by search crews.

Radiation portal monitors detect gamma radiation and are typically used at airports to scan individuals to ensure they do not have radioactive substances on them. Gamma spectrometers measure the intensity of the radiation.

Mr Ray said the new detection equipment could be attached to vehicles so searches could be done from moving vehicles at about 50km/h.

“It will take approximately five days to travel the original route, an estimated 1400km, with crews travelling north and south along Great Northern Highway,” he said.

But by the end of 31 January, the capsule continued to evade search crews.

“More than 660km has been searched so far – thank you to all agencies for their support,” the Department of Fire and Emergency Services said.

So the next morning, when the government revealed the capsule had been found just two metres off the side of the highway at 11:13 local time Wednesday, it seemed the all-but-impossible had been achieved.

Authorities said search crews had “quite literally found the needle in the haystack”.

“You can only imagine it’s a pretty lonely stretch of road from Newman down to Perth,” Fire and Emergency Services Commissioner Darren Klemm said at a press conference on Wednesday.

“You can’t help but imagine there was an element of surprise from the people in the car when the equipment did spike up.”

While hesitant to give the exact location the radioactive capsule was found, Mr Klemm described it as “the best possible outcome”.

Local media reports suggest it was found some 74km from Newman – so around 200km from the mine site.

No one appeared to have been injured by the capsule, according to authorities, and it did not seem to have moved from where it fell.

Mr Klemm said the additional resources from the federal government proved key to finding the capsule.

He said the survey equipment used from the start to detect radioactivity – paired with the specialised equipment that physically located the capsule – is how a car driving past at 70km/h found it.

A check of the serial code on the capsule confirmed it was the right one.

Associate Professor Nigel Marks from Western Australia’s Curtin University hailed the find as a “victory for science”.

“You know it emits gamma radiation so the obvious thing is to comb the side of the road looking for something with a strong gamma signal… and sure enough that’s exactly where they found it.”

Dr Marks added that many “orphan sources” – a self-contained radioactive material – that get lost are generally not recovered.

“A surprisingly large number of these sources that get lost – never get found”, he said.

“It’s a regulatory failure, but I think the way they found it is really cool.”

The chair of Australia’s Radiological Council will now investigate exactly how the capsule was misplaced in the first place.

The outcome of the report will determine whether or not charges are laid against Rio Tinto.

After the capsule was found the Chief Executive of Rio Tinto, Simon Trott, said the company would “fully cooperate” with the investigation.

He added that Rio Tinto would foot the bill for the search if the government requested it.

No classified documents were found during an FBI search of President Joe Biden’s home in Rehoboth, Delaware, his lawyer says.

In a statement, Mr Biden’s attorney said Wednesday’s search was “planned” with the president’s “full support”.

The nearly four-hour search of the property related to a wider probe into the handling of classified documents.

The FBI has not commented on the search. As it was consensual, no search warrant was sought.

Mr Biden’s lawyer, Bob Bauer, said the search was carried out “without advance public notice” in the interests of “operational security and integrity”.

Following the search – which lasted from 0830 to 1200 local time – Mr Bauer said that “no documents with classified markings were found”.

Some “materials and handwritten notes” that appear to date to Mr Biden’s time as vice president between 2009 and 2017 were taken for “further review”, Mr Bauer added.

The search is the latest in a series carried out at various locations, after classified documents were found at the Penn Biden Center – an office space – in Washington DC in November. This was not made public at the time.

More documents were discovered at another of Mr Biden’s homes in Wilmington, Delaware, in searches conducted in December and January.

The precise number of classified records recovered remains unclear – although at least a dozen were found during the January searches alone.

Mr Biden has said his team did “what they should have done” by alerting officials immediately, and that they are “co-operating fully and completely” with the investigation.

After the first of January’s searches, Mr Biden told reporters the files were in a locked garage.

“It’s not like they are sitting in the street,” he said.

The latest search comes a day after special counsel Robert Hur officially began his duties overseeing the probe into the documents.

President Donald Trump and former Vice President Mike Pence have also been embroiled in controversy over the handling of classified documents.

In Mr Pence’s case, a “small number of documents bearing classified markings” were found at his home in Carmel, Indiana, according to a letter sent to the National Archives by his lawyer. The documents were recovered by the FBI from a safe at the property on 19 January, with two boxes more delivered to the Archives on 23 January.

An August 2022 search of Mr Trump’s Mar-a-Lago estate in Florida uncovered dozens of boxes and about 11,000 documents, including about 100 with classified markings.

The search warrant came after attorneys representing Mr Trump had said all government records were returned. Mr Trump has repeatedly denied any wrongdoing and claimed that he had declassified the documents taken with him.

The justice department search of Joe Biden’s holiday home adds one more twist to a classified documents saga that has stretched on for nearly a month now and includes a special counsel overseeing the inquiry.

The FBI move could reveal how forthcoming and thorough the Biden team has been in reviewing the documents stored on his personal property. For the most part, the Biden lawyers have been conducting their own review of the president’s personal residences without government investigators looking over their shoulders. While they found classified material at the president’s Wilmington home, they have said that there were no such documents found at the president’s beach house.

At the very least, the search will help quell some of the concerns expressed by Republicans that the government is holding Mr Biden to a lower level of scrutiny and suspicion than Donald Trump, who had his Mar-a-Lago estate searched by the FBI last August. When Mr Biden’s lawyers first revealed they had found classified material at his home and personal office, the former president, Speaker of the House Kevin McCarthy and other conservatives openly wondered why the current president wasn’t targeted by government investigators as well.

Now, however, Mr Biden’s defenders are pointing out that multiple Biden properties have been searched, but there is no indication that the FBI has investigated Mr Trump’s New Jersey and New York homes.

Ukraine’s defence minister has said Russia is preparing a major new offensive, and warned that it could begin as soon as 24 February.

Oleksii Reznikov said Moscow had amassed thousands of troops and could “try something” to mark the anniversary of the initial invasion last year.

The attack would also mark Russia’s Defender of the Fatherland Day on 23 February, which celebrates the army.

Meanwhile, three people have died in an attack on the city of Kramatorsk.

Seven others were wounded in the city in Donetsk region after a Russian missile struck a residential building, the provincial governor said.

The toll is expected to rise as rescuers comb through the wreckage.

“The only way to stop Russian terrorism is to defeat it,” Mr Zelensky wrote on social media about the attack. “By tanks. Fighter jets. Long-range missiles.”

Ukraine has recently renewed calls for fighter jets to help protect itself from air attacks after Germany, the US and the UK agreed to send them tanks.

Mr Reznikov said Moscow had mobilised some 500,000 troops for the potential offensive.

In September, Russian President Vladimir Putin announced a general mobilisation of some 300,000 conscripted troops, which he said was necessary to ensure the country’s “territorial integrity”.

But Mr Reznikov suggested that the true figure recruited and deployed to Ukraine could be far higher.

“Officially they announced 300,000 but when we see the troops at the borders, according to our assessments it is much more,” he told the French BFM network. The BBC cannot independently verify this figure.

Despite some heavy fighting in the eastern Donbas region, the war has entered something of a stalemate in recent months since Ukraine retook the southern city of Kherson.

With the exception of the Russian seizure of the town of Soledar, neither side has made major territorial advances.

But a Russian spring offensive – and a Ukrainian counter-offensive – has long been considered likely. The US-based Institute for the Study of War (ISW) recently said that Moscow could seek to “undertake a decisive action” and launch a “big offensive” in the east.

Mr Reznikov said Ukraine’s commanders would seek to “stabilise the front and prepare for a counter-offensive” ahead of the rumoured Russian advance.

“I have faith that the year 2023 can be the year of military victory,” he said, adding that Ukraine’s forces “cannot lose the initiative” they have achieved in recent months.

The defence minister was in France to strike a deal to purchase additional MG-200 air defence radars, which he said would “significantly increase the capacity of the armed forces to detect air targets, including winged and ballistic missiles, and drones of various types”.

Mr Reznikov’s comments come as Ukrainian intelligence alleges that President Putin has ordered his forces to seize the Donbas before the end of spring.

But speaking on Monday, Nato Secretary-General Jens Stoltenberg warned that there were no indications that Mr Putin had limited his military goals to seizing eastern regions of Ukraine.

“That they are actively acquiring new weapons, more ammunition, ramping up their own production, but also acquiring more weapons from other authoritarian states like Iran and North Korea,” Mr Stoltenberg said.

“And most of all, we have seen no sign that President Putin has changed his overall goal of this invasion – that is to control a neighbour, to control Ukraine. So as long as this is the case, we need to be prepared for the long haul.”

Meanwhile, Ukraine’s Deputy Defence Minister Hanna Malyar said that intense fighting was continuing in the Donbas region, where Russian forces and Wagner Group mercenaries have been trying to take the town of Bakhmut.

She added that Moscow’s troops were also trying to seize Lyman – the former Russian logistics hub that Ukrainian troops retook in October.

“Russian troops are actively trying to reach the borders of Donetsk and Luhansk regions,” she wrote on the Telegram messaging app. “Our soldiers defend every centimetre of Ukrainian land,” she said.

Speaking on Wednesday night, Mr Zelensky warned that the situation on the front lines of the conflict was testing his forces.

“There is a certain increase in the occupiers’ offensive actions at the front – in the east of our country, Mr Zelensky said. “The situation is becoming even more severe.”

While the Wagner group has claimed it has been heavily involved in Russia’s recent advances in the east, a former commander who fled to Norway has told Reuters that he witnessed the killing and mistreatment of Russian prisoners taken to Ukraine to fight for the group.

Andrei Medvedev made an unverified claim that in the four months he was with Wagner, he saw two people who didn’t want to fight being shot.

About 80% of Wagner’s personnel in Ukraine have been drawn from prisons, according to the US National Security Council.