US President Joe Biden on Wednesday is holding talks with leaders from the Bucharest Nine, NATO's most eastern members, before he departs Poland.
Biden arrived in Warsaw late on Monday following a surprise visit to Kyiv, just days before the one-year anniversary of Russia's invasion of Ukraine.
What is on the agenda?
Biden is due to reaffirm Washington's commitments over the security of the eastern allies and discuss support for Kyiv.
The nine countries have been staunch supporters of military aid to Ukraine and have called for additional assistance to the war-torn country such as air defense systems.
On Tuesday, Lithuanian President Gitanas Nauseda's foreign policy adviser told Lithuanian radio that the leader would seek in the meeting with Biden "greater involvement of the US in Europe, NATO's eastern flank and, of course, more aid to Ukraine."
"Lithuania and other like-minded countries have several requests, which concern air defense, forward defense presence, air defense systems, and greater investments in the defense industry," Asta Skaisgiryte said.
Fears of further Russian agression
The Bucharest Nine grouping came together in response to the 2014 Russian annexation of Crimea from Ukraine. It includes Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia.
The nine countries, who joined NATO after being dominated by Moscow during the Cold War, have had heightened fears that Russian President Vladimir Putin would take military action against them in light of Moscow's invasion of Ukraine.
"When Russia invaded, it wasn't just Ukraine being tested. The whole world faced a test for the ages," Biden said on Tuesday in an address marking nearly one year since Russia launched a war against Ukraine.