Biden warned in an NBC interview with Lester Holt on Thursday that American citizens should "leave now," adding that sending troops during a Russian invasion will be a “world war.”

“It’s not like we’re dealing with a terrorist organization. We’re dealing with one of the largest armies in the world. It’s a very different situation and things could go crazy quickly,” He added.

When questioned if there is any scenario that would push him to send US troops to Ukraine he said “There’s not. That's a world war when Americans and Russia start shooting at one another.”

"We’re in a very different world than we’ve ever been," he added.

Department issued an advisory that the U.S. “will not be able to evacuate U.S. citizens in the event of Russian military action anywhere in Ukraine.” It warned that regular consulate service — including aiding citizens trying to leave the country — would be “severely impacted.”

NBC News said that US military and intelligence assess that the Russian military could launch a full scale invasion with tanks that could potentially reach Kyiv, within 48 hours.

Biden argued that if Putin is "foolish enough to go in, he’s smart enough not to, in fact, do anything that would negatively impact on American citizens."