White House press secretary Jen Psaki pushed back against reporters in the briefing room on Thursday who suggested that elements of Russia’s invasion of Ukraine have gone “unanswered” by the US and pointed to the serious cost sanctions were having on Russia’s economy.

       Ms Psaki faced several questions regarding whether the use of chemical or biological weapons by Moscow’s forces in Ukraine would be a “red line” for the Biden administration or would go “unanswered”, and contended that nothing the Russians had done up until now had gone without a US response.

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       Pointing to the historically-tough sanctions that the Biden administration had placed on Russia’s economy and figures tied to Vladimir Putin, Ms Psaki declared: “We have basically crushed the Russian economy”.

       The press secretary repeatedly refused to say what the specific US response would be in the event that Russia’s military deployed such weapons on the battlefield. Pentagon press secretary John Kirby has stated that there is no evidence to suggest that Russia has done so, but pointed to statements accusing the US and Ukraine of developing such weaponry in the region as a potential pretext that Moscow could use for striking with chemical or biological weapons.

       “We have not let anything go unanswered that President Vladimir Putin has done to date,” said Ms Psaki. Adding of the US response to the potential use of chemical or biological weapons, she said: “What that would look like, I can't give you an assessment of that from here.”

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       Ms Psaki also stressed that President Joe Biden had been clear in his resolve to not utilise US troops to defend Ukrainian soil while facing a barrage of questions about how the US could escalate its support for Ukraine or opposition to Russia.

       The US has deployed thousands of troops around Europe in recent days amid the Russian invasion and stated that the deployments are meant to shore up Nato defences in case Russia’s invasion spreads beyond Ukrainian territory.

       Russia’s Vladimir Putin has laid out a number of preconditions for the end of his invasion, which US officials now say has cost the lives of thousands of Russian soldiers. Moscow has demanded a demilitarisation of Ukraine and a guarantee that it will not join Nato or the European Union, conditions which are likely to be flatly rejected by Ukraine’s government.