French President Emmanuel Macron has said the coming days will be crucial to de-escalating the Ukraine standoff, after a meeting with Russia's Vladimir Putin.
Mr Putin hinted that progress had been made during his first Moscow summit with a Western leader since Russian troops massed on Ukraine's borders.
Moscow has denied any plans to invade.
However, Western powers have become increasingly concerned by the possibility of a conflict.
US officials said on Sunday that Russia has assembled 70% of military forces needed for a full-scale invasion.
On Monday, President Joe Biden met German Chancellor Olaf Scholz in Washington and threatened to shut down a key Russian gas pipeline to Germany if Moscow invaded Ukraine.