US President Joe Biden is expected to lay out his view of the war in Ukraine as a battle for democracy during a speech later on Tuesday.
He will make his address in the Polish capital, Warsaw – a day after his surprise visit to Ukraine.
His speech comes hours after Russia’s Vladimir Putin announced Moscow was suspending participation in a key arms control treaty with the US.
He made the announcement in his state of the nation address.
The leaders’ competing speeches come days before the first anniversary of Russia’s full-scale invasion of Ukraine.
In Warsaw, the US president is expected to stress the vital role the United States has played in galvanising Western backing for Ukraine against Russian aggression.
But he will also be looking to shore up support for his policy at home, where some politicians are expressing doubts about the scale of US involvement.
In his speech a stone’s throw from the Kremlin, President Putin again blamed the West for Russia’s invasion, complaining of Western hypocrisy and of withdrawing from “fundamental agreements”.
“I want to repeat: it is they who are culpable for the war, and we are using force to stop it,” he said to great applause.
Mr Putin also reiterated his unfounded claim that Moscow had been facing a neo-Nazi threat from Ukraine, which he used as justification to launch his “special military operation”.
He said Russia would suspend its participation in the New Start treaty – the last remaining nuclear arms deal between Russia and the US – adding: “No-one should be under the illusion that global strategic parity can be violated.”
Ahead of his address, US President Joe Biden will meet Poland’s leader, Andrzej Duda, and other central European allies to discuss bilateral cooperation and to strengthen Nato against aggression.
That’s after the president met his Ukrainian counterpart, Volodymyr Zelensky, in Kyiv on Monday – telling a press conference that the US will back Ukraine for “as long as it takes”.
“We have every confidence you’re going to continue to prevail,” he said.
The pair also visited a memorial to soldiers who have died in the nine years since Russia annexed Crimea and its proxy forces captured parts of the eastern Donbas region.
After the visit, US Secretary of State Antony Blinken announced a new package of security assistance for Ukraine valued at $450m (£373m), as well as an extra $10m in emergency assistance to maintain Ukraine’s energy infrastructure.
A new wave of sanctions against individuals and companies “that are trying to evade or backfill Russia’s war machine” will also be announced later this week.
The US is one of Ukraine’s biggest allies and has already given billions of dollars in military assistance.
Mr Biden recently announced that the US would send 31 battle tanks and longer-range missiles but has stopped short so far of sending F-16 fighter jets, despite repeated calls for them from Ukraine.
However, Mr Zelensky on Monday said that he had discussed with Joe Biden the possibility of the US sending other weapons.