U.S. President Joe Biden believes Ukraine is unlikely to join NATO anytime soon but it would not be possible to agree it would never happen.

Biden said he expects Russian President Vladimir Putin to "move in" on Ukraine as Russia continues to build up troops on the border and neither the U.S.-led NATO nor Russia appears to be ready to cede to the other's demands, Nikkei Asia reports.

"I'm not sure he ... is certain about what he's going to do," Biden said in a news conference, his first such solo appearance at the White House since last March. "My guess is he will move in -- he has to do something."

Biden began with an address touting the accomplishments of his administration's first year in office before taking questions from journalists for nearly two hours on a range of issues from his stalled legislative agenda to foreign policy.

Biden said he believes that Putin does not want a full-blown war but will test the U.S. and NATO as much as he can -- and that he will face severe consequences for doing so. The American leader indicated that there is room to work with Putin regarding demands like no strategic weapons to be stationed in Ukraine and that Ukraine is unlikely to join NATO anytime soon but it would not be possible to agree it would never happen.

"So there's room to work if he wants to do that," Biden said.