President Biden made clear Tuesday that there would not "be any American forces moving into Ukraine," though U.S. troops could be moved to Europe in the "near term." The troops may head to NATO front-line countries if Russian begins a large military operation against Ukraine.

Biden's comments to reporters in Washington come as the White House has urged Americans to leave Ukraine, saying that the security situation in the region "can deteriorate with little notice."

"There are reports Russia is planning significant military action against Ukraine. The security conditions, particularly along Ukraine’s borders, in Russia-occupied Crimea, and in Russia-controlled eastern Ukraine, are unpredictable and can deteriorate with little notice," said a State Department travel advisory Sunday.

Joe Biden at the White House in Washington in press conference marking first year in office

President Joe Biden (Chip Somodevilla/Getty Images)

The president compared a possible Russian invasion of Ukraine to the kind of operation not seen in Europe since World War II, saying the country would face "enormous consequences" if it attacked its neighbor. 

"There will be enormous consequences if he were to go and invade … for Russia," Biden said when asked to assess the risk that Russian President Vladimir Putin would opt to invade Ukraine. "Not only in terms of economic consequences and political consequences, but there would be enormous consequences worldwide."

STATE DEPARTMENT ISSUES ‘DO NOT TRAVEL’ WARNING FOR UKRAINE AS EMBASSY STAFF IS TOLD TO LEAVE 

Biden said that such an invasion would "change the world," comparing the scope of the situation to World War II.

"If he were to move in with all those forces, it would be the largest invasion since World War II," Biden said.

Vladimir Putin

Vladimir President Vladimir Putin (Sputnik, Kremlin Pool Photo via AP)

The president said trying to predict what Putin will do is like "reading tea leaves," noting that it will ultimately be Putin's decision on what to do with all the troops Russia has amassed on the Ukrainian border.

Ukraine volunteer forces

Members of Ukraine's Territorial Defense Forces, volunteer military units of the Armed Forces, train in a city park in Kyiv, Ukraine. (AP/Efrem Lukatsky)

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But officials in Ukraine have sought to calm fears that an invasion could be imminent, arguing that the situation is currently "under control."

"There are risky scenarios. They’re possible and probable in the future," Ukrainian Defense Minister Oleksii Reznikov said Monday. "But as of today ... such a threat doesn’t exist."