US President Joe Biden said on Tuesday that he would consider personally sanctioning Russian President Vladimir Putin if Russia invades Ukraine.

"If he were to move in with all those forces, it would be the largest invasion since World War II. It would change the world," Biden told reporters at an unannounced stop at a local business in Washington, according to ABC News.

Asked about what would lead him to deploy troops staging nearby, Biden said that depends on "what Putin does or doesn't do" but he repeated that American forces would not move into Ukraine.

"I may be moving some of those troops in the nearer term, just because it takes time," Biden said, adding it's not to be "provocative" but to reassure NATO allies whom have reasons for concern.

"We have no intention of putting American forces, or NATO forces, in Ukraine. But we -- as I said -- they're gonna be serious economic consequences if he [Putin] moves," Biden added.

On Monday, the Pentagon announced that Defense Secretary Lloyd Austin had placed around 8,500 US-based troops on "heightened alert" for rapid deployment to assist NATO if needed.

No decision to deploy them had been made, though, according to Pentagon spokesman John Kirby, who noted that the US could also offer troops already stationed in Europe.

Later in the day, Biden held a video call with the leaders of the European Commission, European Council, NATO, France, Germany, Italy, Poland and the United Kingdom.

The White House said the call lasted 1 hour and 20 minutes.

The conversation came a day after the State Department ordered the families of all American personnel at the US Embassy in Ukraine to leave the country amid heightened fears of a Russian invasion.

The department told the dependents of staffers at the US Embassy in Kiev that they must leave the country. It also said that non-essential embassy staff could leave Ukraine at government expense.

Hours later, the State Department warned American citizens not to travel to Russia amid tensions with Ukraine.

“Do not travel to Russia due to ongoing tension along the border with Ukraine, the potential for harassment against US citizens, the embassy’s limited ability to assist US citizens in Russia, COVID-19 and related entry restrictions, terrorism, harassment by Russian government security officials, and the arbitrary enforcement of local law,” the warning read.

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