The US and Russia are preparing for talks on Tuesday as tensions grow over Ukraine.
US President Joe Biden and Russian leader Vladimir Putin will speak in a video call.
It comes after a build-up of Russian troops on the Ukrainian border – believed to be a signal of a potential invasion.
Russia is adamant that the US should guarantee that Ukraine will not be admitted to the NATO military alliance.
US intelligence officials, meanwhile, have determined that Russia has massed about 70,000 troops near its border with Ukraine and has begun planning for a possible invasion as soon as early next year, according to a Biden administration official.
On Friday, Mr Biden said: "What I am doing is putting together what I believe to be, will be, the most comprehensive and meaningful set of initiatives to make it very, very difficult for Mr Putin to go ahead and do what people are worried he may do."
Ukrainian officials have said Russia could invade next month.
The country's defence minister, Oleksii Reznikov, said the number of Russian troops near Ukraine and in Russia-annexed Crimea is estimated at 94,300, and warned that a "large-scale escalation" is possible in January.