US president Joe Biden is expected to express strong concerns about a Russian military build-up on its border with Ukraine when he holds talks with President Vladimir Putin of Russia on Tuesday.
In the video call Mr Biden is expected to set out again the support of the US for the sovereignty and territorial integrity of Ukraine.
There is concern in Washington that the build-up of Russian forces close to Ukraine could be a prelude to an invasion.
Last week US officials suggested that intelligence services believed Russia could be planning a multi-front offensive against Ukraine as soon as early next year involving up to 175,000 troops.
US media has reported that the Kremlin is seeking written guarantees from the Americans and its allies that the Nato military alliance will not expand further east to take in Ukraine as a member or to host Western forces.
The White House said ahead of the talks that Mr Biden and Mr Putin would discuss a range of topics in the US-Russia relationship, including strategic stability, cyber, and regional issues. However, it said Mr Biden would "underscore US concerns with Russian military activities on the border with Ukraine".
Low point
The talks on Tuesday come at a particularly low point in relations between the US and Russia.
The US has indicated that Russia would face “serious consequences” if it engaged in military action against Ukraine.
There have been suggestions in the US that this could involve financial sanctions that would cut Russia off from the global financial system.
US media reported on Monday that Mr Putin was expected to table his proposals for a guarantee that Nato would not expand eastward at the talks on Tuesday.
In a speech last month Mr Putin argued that the West had a “superficial approach to our warnings about red lines”.
He said the US and its allies supplied lethal weapons to Ukraine, conducted “provocative” military exercises in the Black Sea and flew strategic bombers just 20km from Russia’s borders.
He has also warned the US against stationing missile-defence systems in Ukraine similar to those in Romania and Poland, claiming that they could be secret offensive weapons capable of reaching Moscow within 10 minutes.
Conflict
After Ukraine’s pro-Western revolution in 2014, Russia invaded and then annexed the peninsula of Crimea, which is part of Ukraine. The West believes that Russia subsequently provoked a conflict in the east of Ukraine that is still running.
The US offered last week to mediate between Russia and Ukraine on ending the seven-year war between Ukrainian government forces and Russian-backed separatists .
Mr Biden and Mr Putin last met in June in Geneva. The talks then did not lead to major breakthroughs but did result in more communication between the White House and the Kremlin. A number of top Biden administration officials have visited Moscow in recent months.
