WARSAW (AP) President Joe Biden said Wednesday that Russian President Vladimir Putin made a big mistake by suspending his countrys participation in the last remaining U.S.-Russia nuclear arms control treaty. The U.S. president was in Poland to reassure eastern flank NATO allies that the U.S. will remain by their sides amid the grinding Russian invasion of Ukraine.

In his first comments since Putins announcement Tuesday, Biden condemned the Russian decision to pull back from the treaty, known as New START. The decision to suspend Russian cooperation with the treatys nuclear warhead and missile inspections follows Moscows cancellation late last year of talks that had been intended to salvage an agreement that both sides have accused the other of violating.

Bidens comments came as he was wrapping up a whirlwind, four-day visit to Poland and Ukraine with talks with leaders from the Bucharest Nine, a collection of nations in the most eastern parts of the NATO alliance that came together in response to Putins 2014 annexation of Crimea from Ukraine.