BUCHAREST, Romania — U.S. President Joe Biden will join a meeting by video link of presidents of countries on NATO's eastern flank being held Monday in the Romanian capital, according to the offices of the Romanian and Polish presidents.

The presidents gathering represent the so-called Bucharest Nine, a group of the easternmost members of the Western military alliance. Most of them share a concern about Russia's attempts to reassert its influence over their region, their anxieties growing after Russia annexed Ukraine's Crimean Peninsula in 2014.

Romanian President Klaus Iohannis, the host, said on Twitter  that he was glad to be welcoming Biden, and that the meeting was in preparation for a full NATO summit next month. 

He said Monday's meeting, co-hosted with Polish President Andrzej Duda, would include discussions of defense and deterrence on the alliance's Eastern flank, and that NATO Secretary General Jens Stoltenberg was also participating.

Duda said at a news briefing before the meeting that Ukraine would also be a focus of discussions. He said he was relieved that Russia had pulled back many of the forces that it had recently deployed to near the Ukrainian border, saying he believed that reduced the risk of another Russian invasion.

"But there is no doubt that the situation there is very difficult, that Ukrainian territory is occupied," Duda said at a news briefing alongside Iohannis.

"Neither Europe nor the world can take their eyes off this part of our continent," Duda said. "We must all absolutely support Ukraine on the one hand, but on the other hand, we must also guard our security, because this is our eastern flank, both for Romania and for Poland."

The members of the Bucharest Nine are Romania, Poland, Hungary, Bulgaria, the Czech Republic, Slovakia, and the three small Baltic states of Estonia, Latvia and Lithuania. 

These countries were all controlled by Moscow during the cold war, with the Baltic states incorporated into the Soviet Union. 

Today they are all members of the Europe Union and NATO, with the military alliance increasing its military presence in the region after Russia's invasion of Ukraine.

On Tuesday, Iohannis and Duda will attend a military exercise involving Polish and Romanian troops called "Justice Sword 21" taking place in Smardan, in eastern Romania.

The meeting of the nine central and eastern European nations comes ahead of a full NATO summit on June 14 in Brussels, where the alliance has its headquarters.

At the June summit, Biden and other leaders plan to discuss tense ties with Russia and China, the troop withdrawal from Afghanistan and the future of the 30-nation alliance.