Russian forces are arriving at the Ukraine border, said Sullivan, declining to share additional intelligence. He added that President Biden has spoken with global leaders from Canada, the U.K., France, Germany, Italy, Poland, Romania, NATO, the European Commission, and the European Council about potential responses to the situation.

U.S. oil prices jumped to a seven-year high on the news. Major U.S. defense stocks and commodities like Northrop Grumman and Lockheed Martin also went up after the press conference on Friday afternoon, while the RSX Russia ETF plunged.

World leaders have objected to the Russian military buildup but differ in their views on the intentions of Russian President Vladimir Putin. Russia has publicly said that it does not intend to start a war but that it will defend its interest in Ukraine.

U.S. intelligence officials initially thought that Putin would hold his troops until the Winter Olympics in Beijing ended on Feb. 20, to avoid agitating Chinese President Xi Jinping, a key ally. On Friday, Sullivan said that the timeline for a potential Russian invasion had accelerated. 

“I do want to be clear: It could begin during the Olympics despite a lot of speculation that it would only happen after the Olympics,” Sullivan told reporters, adding, “Any Americans in Ukraine should leave as soon as possible, and in any event, in the next 24 to 48 hours.”

Sullivan said that Russia would likely begin its invasion through air raids before continuing with ground troops, which would cut off access to escape from the country by road, rail, and air. An invasion of Ukraine, he said, could lead to the potential deaths of 25,000 to 50,000 civilians, 5,000 to 25,000 members of the Ukrainian military, and 3,000 to 10,000 members of the Russian military. 

The White House said it would not send American troops to aid in the evacuation of Americans left in Ukraine. “The president will not be putting the lives of our men and women in uniform at risk by sending them into a war zone to rescue people who could have left by now, but chose not to,” Sullivan said. 

On Thursday evening President Biden said in an interview with Lester Holt of NBC News that sending troops into the country would cause “a world war when Americans and Russia start shooting at one another.”

“We’re in a very different world than we’ve ever been,” Biden added.

The U.S. on Friday ordered 3,000 additional troops to deploy to Poland within the next few days. Those troops will join 3,000 others who have already been ordered to Poland and Romania. Sullivan said the buildup is “defensive in nature” and meant to deter Putin from making the decision to invade.

Ukraine’s military said on Friday that Russian-backed separatists in the country’s east are practicing military exercises and the country is nearly encircled by hostile forces.