GENEVA: The top diplomats of Russia and the United States played down any prospect of quickly resolving their differences over Ukraine at talks they began in Switzerland on Friday, but the US side still hoped the meeting could de-escalate soaring tensions.

US Secretary of State Antony Blinken shook hands with Russian Foreign Minister Sergei Lavrov in the Hotel President Wilson where their meeting is taking place, before they sat down to talk.

Lavrov told Blinken he did not expect a breakthrough at the Geneva talks.

"(Our) proposals are extremely concrete and we await equally concrete answers," Lavrov said.

"This is a critical moment. You're right: We don't expect to resolve our differences here today," Blinken said in his opening remarks.

"But I do hope and expect that we can test whether the path of diplomacy, of dialogue remains open. We’re committed to walking that path, to resolving our differences peacefully and I hope to test that proposition today," Blinken added.

Washington’s hopes of building a united front of opposition to Moscow were complicated by US President Joe Biden's comments at a news conference on Wednesday in which he predicted Russia would "move in" on Ukraine and said Moscow would pay dearly.

"President Biden's remarks were not helpful, even if he corrected himself later," said Thomas Kleine-Brockhoff, vice president at the Berlin office of The German Marshall Fund of the United States.

Russia has massed tens of thousands of troops on its borders with Ukraine, and Western states fear Moscow is planning a new assault on a country it invaded in 2014 to annex the Crimean peninsula. Russia denies it is planning an attack, but says it could take unspecified military action if a list of demands are not met, including a promise from NATO never to admit Ukraine.

Asked by CBS News if Russia was intimidated by Ukraine, Deputy Foreign Minister Sergei Ryabkov said on arriving for the talks on a cold and blustery day in Geneva: "We're not afraid of anyone, even not of the US."

In Moscow, the Kremlin reacted coolly to a Russian parliament initiative to recognise two pro-Russian breakaway regions in eastern Ukraine as independent states, saying it was important to avoid steps that could increase tensions.

Kremlin spokesperson Dmitry Peskov said it was important not to try and score political points in such a fragile situation.

The Kremlin was not expecting Blinken to hand over a written response to Russia's sweeping demands for security guarantees from the West on Friday, Peskov said.

Russia wants NATO to promise not to admit Ukraine as a member and halt its eastward expansion. The US-led alliance has rejected that.