Brussels: As the fourth round of talks resume between Russia and Ukraine, NATO is concerned about Russia carrying out a chemical attack in Ukraine, secretary general Jens Stoltenberg said on Tuesday.


"We are concerned that Moscow could stage a false flag operation possibly including chemical weapons," said the NATO chief ahead of the alliance's defence ministers meet, according to AFP. The NATO chief cited "absurd claims" from Russia that Ukraine possesses biological weapons labs.


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While noting that NATO remains "very vigilant" on that risk, the Stoltenberg stressed that Russia would have "a high price to pay" if it carried out such a "violation of international law".


The NATO chief refused to "speculate about any military response from the NATO side" if such a chemical attack happened.


The meeting on Wednesday is aimed to cover "concrete measures to reinforce our security for the longer term in all domains" to adapt to the changed threat environment arising from Russia's "senseless war".


"This could include substantially more forces in the eastern part of the alliance at higher readiness and with more pre-positioned equipment," on top of the bolstered NATO forces already sent to NATO countries bordering Ukraine, he added.


Meanwhile, NATO leaders expected to meet in a long-scheduled summit in June in Madrid to look at longer-term changes for the alliance.


"It's important to distinguish greatly about the immediate response -- all the tens of thousands more troops, air power and naval power -- and then the more long-term adjustment or posture," to be discussed in June, he said.


Sharing the details of the losses, Ukraine’s ministry of foreign affairs noted that more than 13,500 Russian troops have been killed with 404 Russian tanks being destroyed since Russia began its war on Ukraine.