Ukraine round-up: Russia sets gas deadline for West and troops leave Chernobyl.

More than five weeks into Russia's war on Ukraine, Moscow has threatened to cut off Western nations from natural gas supplies - something that could affect energy prices across Europe.
Vladimir Putin has followed through on weeks of threats by signing a decree that foreign countries they must start paying for gas in Russian roubles or it will halt supplies.
And those new rules start on Friday, meaning Western nations were effectively handed a midnight deadline to comply.
"Nobody sells us anything for free, and we are not going to do charity either - that is, existing contracts will be stopped," the Russian president said.
Many payments for April gas deliveries are reportedly not due until later in the month, so it is not thought that there is an immediate threat to supplies.
It is also still unclear whether the new payment mechanism set out by Russia would fully ban euros.
But France and Germany condemned Mr Putin's demands as being akin to "blackmail".
Western companies and governments have previously rejected Russia's demands to pay for gas in roubles as a breach of existing contracts, which are set in euros or US dollars.
Yet the EU gets about 40% of its gas and 30% of its oil from Russia, and there is no ready-to-go replacement.
Notably, the EU did not enact sanctions on Russian fuel supplies - even though other Western nations such as the US and Canada did.
Mr Putin's demand to be paid in roubles is widely seen as an attempt to boost the currency, which has been hit by the wide range of international sanctions that followed the invasion of Ukraine.
Read the full story about the midnight gas deadline here.
'Most Russian troops' leaving Chernobyl, Ukraine says
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Many Russian troops occupying the former nuclear power plant at Chernobyl have left, Ukraine's state nuclear operator has said.
Energoatom said two columns of Russian forces had set off towards the Belarusian border on Thursday morning, leaving just a few soldiers at the site.
Several days ago the mayor of Slavutych, a nearby town housing workers at the plant, announced that Russian troops had also left the town.
The withdrawal follows reports that some Russian soldiers are being treated for radiation poisoning in Belarus after spending time in the most contaminated part of the Chernobyl exclusion zone.
The International Atomic Energy Agency said it was investigating the report.
Russia's occupation of the site since 24 February, the day of the invasion, has been dogged with concerns about power outages and problems for the staff, many of whom were trapped there for weeks and could not get home.
It is the site of what is considered to be the world's worst nuclear accident in 1986, and while no longer a working power station, Chernobyl still requires constant management.
Russia "redeploying" not retreating
Troops leaving some occupied areas might sound like a win for Ukraine, but Western intelligence warns that Russia is redeploying, rather than retreating.
"Russia is trying to regroup, resupply and reinforce," Nato Secretary General Jens Stoltenberg said.
Russia said earlier this week that it was planning to "radically" reduce its military activity in some places - such as near the capital Kyiv or the city of Chernihiv - and concentrate on the eastern Donbas region.
Shelling continues on cities, including those Russia suggested it would reduce its assault on, but Mr Stoltenberg said Nato can see Russia re-positioning troops.
Echoing Mr Stoltenberg's remarks, the UK's Defence Secretary warned that Russia's change in tactics was "not a retreat", and that it was "changing its focus" after its first efforts were rebutted.
Read more about the change in plans here.
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Mariupol evacuation delayed, Red Cross says
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The evacuation of thousands of civilians from the besieged south-eastern city of Mariupol has been delayed until Friday, the Red Cross has said.
Ukrainian Deputy Prime Minister Iryna Vereshchuk said a convoy of 45 Ukrainian buses was on its way to the port city, but humanitarian officials said the operation had been delayed for security and logistical concerns.
One resident of the city, Yevgen, described the humanitarian disaster civilians have faced to the BBC.
"It was constant bombing," he said.
"Planes went past every 10 minutes and dropped bombs on Mariupol.
People were falling and dying in front of my eyes.
We buried people in gardens."
Another resident, Natalia, said Russia soldiers have been infiltrating the city and offering food to civilians in a PR campaign.
"Some people couldn't resist taking them, because they hadn't eaten for several days," she said.
"When you're suffering like that, you'll take anything."
French intelligence chief fired over Russian war failings
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The head of French military intelligence, Gen Eric Vidaud, is set to lose his job after failing to predict Russia's war in Ukraine, French media has reported.
Seven months after he took on the role, one report said he was blamed for "inadequate briefings" and a "lack of mastery of subjects".
The US correctly assessed that Russia was planning a large-scale invasion, while France concluded it was unlikely.
In early March, Gen Burkhard acknowledged that French intelligence had not been up to the level of US or UK briefings, which were publicised to pile pressure on Russia's Vladimir Putin.
"The Americans said that the Russians were going to attack, they were right," he told Le Monde newspaper.
"Our services thought instead that the cost of conquering Ukraine would have been monstrous and the Russians had other options" to bring down the government of Ukraine's Volodymyr Zelensky, he added.
Are tech companies removing evidence of war crimes?
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Social media companies are used to pulling down vast amounts of content that break the rules, erasing it from the internet.
They're expected to do so, by governments and regulators.
But what happens when efficient artificial intelligence moderators are removing evidence of possible war crimes, sweeping it away from investigators' eyes?
TikTok, for example, does not allow "shock value" or violence, or anything that is "gratuitously" sadistic or gruesome.
But Ukrainians uploading videos from the ground could be generating more than "likes", BBC technology reporter James Clayton writes.
They may well be uploading a piece in a jigsaw of evidence that will one day be used to prosecute war crimes.