Western officials have “serious concerns” that Russia could use chemical weapons in Ukraine, it emerged today.
Worries are mounting among allied governments after Moscow was seen “setting the scene” for such an attack.
It comes as the UK prepares to send anti-aircraft missiles to Ukraine, after the country accused Russia of a litany of attacks on its civilians - including targeting a children's and maternity hospital in Mariupol.
A Western official, who spoke on condition of anonymity, said: “We’re seeing some of the disinformation come out of Moscow about non-conventional weapons.
“We saw this in Syria, the Russians starting that talk when they or their proxies were about to use those weapons there.”
Asked if there are concerns the Russia will use chemical weapons, they replied: “We have good reason to be concerned about the possible use of non conventional weapons.
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“Partly because we’ve seen what has happened in other theatres, for example in Syria, partly because we see a bit of setting the scene for that in the false flag claims that are coming out, and some other indications as well.
“So it’s a serious concern for us.”
Russia-backed Syria was repeatedly accused of using chemical weapons in the country's bloody war, but Russia vetoed a 2017 UN resolution that would have looked into who was responsible.
The Organisation for the Prohibition of Chemical Weapons found people were exposed to sarin gas in 2017 in the Khan Shaykhun area but did not identify who was responsible.
It comes after the UK Defence Secretary said Britain is considering sending Starstreak anti-air missiles to Ukraine to help the country defend its skies. It's understood the possibility was subject to review with no decisions made so far.
Ben Wallace said the estimated number of Ukrainian civilians killed or injured is more than 1,000 - and warned "worse is likely to come".
Ukraine is facing "its darkest hour" after more than 2million refugees fled over the border, but Britain is proving increased defensive support to the country's forces, he said.
But Mr Wallace once again ruled out a no-fly zone, saying it could hamper Ukrainian efforts to deal with Russian artillery and missiles.
UK Prime Minister Boris Johnson branded Russia "depraved" after Ukraine accused Putin's forces of bombing a children's and maternity hospital in the besieged port of Mariupol - during a supposed ceasefire to let civilians escape.
The city council warned "the destruction is colossal", while President Volodymr Zelensky called it an "atrocity".
Mr Johnson tweeted: "There are few things more depraved than targeting the vulnerable and defenceless.
"The UK is exploring more support for Ukraine to defend against airstrikes and we will hold Putin to account for his terrible crimes."
Germany said it will not send warplanes to Ukraine, after the US rejected an offer by Poland to transfer its Russian-made MiG-29 jets to Ukraine via a US base in Germany.
The plan was plunged into disarray after the White House vetoed an attempt by Warsaw to hand over a fleet of MiG-29s to the Ukrainian air force amid fears it would draw NATO into a direct conflict.
Officials drew a distinction between anti-aircraft missiles and sending jets - saying missiles can only be used defensively, not offensively.
Western officials say Russia’s military advance remains “very slow” with “minimal progress” over the last 24 hours - partly due to the Ukrainians’ resistance and partly due to logistical and execution problems with Russian troops.
But they still fear Vladimir Putin could “flatten Ukraine” despite his war ultimately ending in failure.
An official said: “I think it will end badly for Putin. That doesn’t mean it ends well for Ukraine at all.
“This could end very badly for both. And saying it ends badly for Putin does not mean the Russians not getting into Kyiv, or doing fantastic damage to it with appalling humanitarian costs along the way.”
Officials remain “very concerned about risk of escalation”, with leaders in the Western Balkans “very tense” and worried about “where Russia might go next”.
Western officials also poured cold water on any breakthrough from peace talks, saying it is “hard to say at the moment if there is any real traction or any possibility of serious progress.”
They recalled Putin’s nuclear threat earlier in the war, and said the humanitarian situation is “terrible and getting worse” with the Russians “manipulating offers of ceasefires and corridors”.
UK's 12-point sanctions plan against Russia
1 Shutting off Russian banks’ access to the West, with plan to move to full asset freeze on all Russian banks.
2 Sanctions on Russian central bank and financial institutions, already in effect.
3 Preventing Russian firms and the Russian state raising debt in the UK, already enacted.
4 Asset freeze against individual oligarchs, with 15 so far including Putin and Lavrov and more to come.
5 Targeting key strategic sectors including defence with more planned on services and energy.
6 Blocking access to SWIFT, with UK still pushing for a full SWIFT ban against all Russian banks.
7 Banning Russian planes and ships landing in UK, with new laws next week to put this on longer-term footing.
8 Banning export to Russia of ‘dual-use’ items such as electronics that could be used in military computers or weaponry.
9 Setting a £50,000 limit on wealthy Russians’ deposits in UK bank accounts.
10 Extending the above sanctions to Belarus due to its role supporting the Russian invasion.
11 Extending UK-Crimea total trade embargo to the Luhansk and Donetsk ‘People’s Republics’. But still no date, due to concerns about protecting Ukrainians still there.
12 Sanctions on all members of Russian Parliament and Russian National Security who voted in support of invasion. Still in progress despite EU acting already.
For more information click here.
The comes as Britain prepares to announce further sanctions against Russian oligarchs in the coming days.
An Economic Crime Bill originally designed for other purposes is being hurriedly rushed through Parliament to allow the UK to match sanctions from the EU and US.
But Boris Johnson is facing furious pressure, including from his own party, to announce a more "humane" system for Ukraine refugees to settle in the UK.
Fewer than 1,000 UK visas for Ukrainians with family in Britain had been awarded by this lunchtime out of more than 2million refugees.
And while a 'pop-up' visa centre will start processing applications tomorrow morning in Lille, there is no centre in Calais where Ukrainians with UK links have ended up. The Lille centre will be limited to Ukrainians who have been referred directly to it by Border Force.
The Mirror understands 100 soldiers will now be sent to help Home Office staff in Europe speed up visa applications.
Britain will have two systems. Ukrainians with family in the UK can live and work in the country freely for at least three years.
Those without family links will be able to come in for 12 months under a sponsorship scheme, but its details will only be confirmed later this week.
Boris Johnson said today the second route will allow "everybody in this country" to "offer a home to people fleeing Ukraine".
But Downing Street stopped short of saying individual families will definitely be able to offer a spare room in their home to a Ukrainian.
Sources told the Mirror key details were still being thrashed out, including whether refugees will need the address where they will stay confirmed before they are awarded a humanitarian visa.