President Joe Biden has made it very clear that the Americans are not willing to fight, even though the Russians clearly are.

"Let me be clear: These are totally defensive moves on our part. We have no intention of fighting Russia," Biden said.

As Biden announced new sanctions on Russia on Thursday, he said, "Our forces are not and will not be engaged in the conflict."

He added, "Our forces are not going to Europe to fight in Ukraine but to defend our NATO allies and reassure those allies in the east."

Biden doesn't want to spark a "world war" by risking a direct clash between American and Russian troops in Ukraine, and he's been open about that.

"It's not like we're dealing with a terrorist organisation," the president told NBC earlier this month. "We're dealing with one of the largest armies in the world. This is a complicated situation, and things could go crazy quickly."

While Biden has pledged not to send US troops to Ukraine, the US has sent additional troops and fighter jets to eastern European countries, including Poland and Romania, in recent weeks and announced the deployment of 7,000 additional troops to Germany on Thursday.

"If he did move into Nato countries," Biden has said, "we will be involved."