Biden on Russia-Ukraine escalations: ‘Things could go crazy quickly’

President Biden said in an interview that aired Thursday that tensions between Russia and Ukraine could escalate fast, warning Americans again to leave Ukraine.

“It’s not like we’re dealing with a terrorist organization. We’re dealing with one of the largest Army’s in the world. It’s a very different situation and things could go crazy quickly,” Biden told NBC News’ Lester Holt in his first sit-down interview of the year.

Biden said he has indicated to the Kremlin that there could be repercussions if any Americans are harmed.

“I’m hoping if in fact he’s foolish enough to go in, he’s smart enough not to, in fact, do anything that would negatively impact on American citizens,” he said.

When asked if he has ever told Putin that directly, Biden said he’s been clear on the subject. 

“I didn’t have to tell him that, I’ve spoken about that. He knows that and you know, it’s a little bit. Look, what I’ve asked is, American citizens should leave, should leave now,” Biden said.

U.S. F-15 fighter jets arrived in Poland on Thursday as the U.S. and its NATO allies seek to bolster defenses ahead of what diplomatic and defense officials warn is a potential military conflict between Russia and Ukraine.

Russia has amassed over 100,000 troops near the Ukrainian border, sparking fears that Putin will launch a military offensive.

American troops first landed near the Poland-Ukraine border on Saturday, and the Pentagon said a couple hundred more arrived in Poland on Monday, with plans for additional troops to arrive this week.