In Warsaw, when asked about Putin's statement in regard to the New Start treaty by journalist, Biden sufficed by saying that it was a "big mistake". 

Biden made the brief remark in Warsaw before meeting with the leaders of six nations on NATO's eastern flank to discuss support for Kiev.

When first presented with the question, Biden dismissed it saying he didn't have time. After a pause, Biden described it as a "big mistake". 

Russia's suspension of the treaty was announced during Biden's busy diplomatic visits to eastern Europe to liaise with the leaders of NATO member states. 

The New START pact (Strategic Arms Reduction Treaty), first signed in April 2010, prohibits the United States and Russia from possessing more than 1,550 nuclear warheads on delivery systems. The bilateral treaty effectively serves as a treaty for the non-proliferation of nuclear weapons between the two major powers under a set of conditions that ensure the safety of both parties. 

Read more: Putin announces Russia suspends New START nuke pact participation

In his state-of-the-nation address, Russian President Vladimir Putin reveals that Russia is suspending its participation in the New START treaty.

Later that day, the Russian Foreign Ministry issued a statement as a follow-up. The FM statement clarified that Moscow will be assessing the limitations resulting from the New START nuclear treaty rather than immediately rendering it null.

Read more: US, NATO, EU 'concerned' about Russia decision to suspend New START

The statement clarified that the decision isn't final however reversing it would be conditioned upon a positive change in Washington's attitudes towards Moscow.

Today, the Russian State Duma approved a bill proposed by Russian President Vladimir Putin to suspend Moscow's membership in the Strategic Arms Reduction Treaty.