US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov are meeting for talks in Geneva amid mounting fears that Russia could be about to invade Ukraine.
On Thursday Mr Blinken warned Moscow of grave consequences if any of its forces crossed the border.
Russia has 100,000 troops at the border, but denies planning to invade.
President Vladimir Putin has issued demands to the West, including that Ukraine be stopped from joining Nato.
He wants the Western defensive alliance to abandon military exercises and stop sending weapons to eastern Europe, which Moscow sees as its backyard.
Russia previously seized and annexed the Crimean peninsula in southern Ukraine in 2014. Ever since, Ukraine’s military has been locked in a war with Russian-backed rebels in areas near the border. The conflict has claimed 14,000 lives and caused at least two million people to flee their homes.
The summit between the top US and Russian diplomats follows moves by Mr Blinken to secure US allies’ backing for sanctions against Moscow.
After discussions in Berlin with British, French and German officials on Thursday, Mr Blinken said that allowing a Russian incursion into Ukraine would “drag us all back to a much more dangerous and unstable time, when this continent, and this city, were divided in two… with the threat of all-out war hanging over everyone’s heads”.
Tensions over Ukraine
What do the US and Russia want from these talks?
It’s highly possible that Mr Blinken and Mr Lavrov will emerge from the talks, which are expected to last about two hours, with differing accounts of what took place.
State Department officials have said Mr Blinken will seek to offer Mr Lavrov a “diplomatic off-ramp” to ease tensions.
The US has rejected Russia’s red lines, but is willing to discuss Mr Putin’s security concerns.
For its part, the Kremlin says the diplomats will take stock of talks so far on the Ukraine crisis, and that Russia is not expecting the US to provide a formal response to its proposals.
Russia’s Deputy Foreign Minister Sergei Ryabkov said on Friday that ties with the US are nearing a “dangerous critical line”, according to Russia’s Interfax news agency. He said Moscow hoped to persuade Washington to change its approach.
Mr Blinken could offer Russia more transparency on military exercises in the region, or suggest reviving restrictions on missiles in Europe. These rules were previously set out in the Intermediate-Range Nuclear Forces Treaty, a Cold War-era pact that the US scrapped in 2019, after accusing Russia of violating the deal.
Russia maintains that Ukraine is its primary focus. On Thursday it unveiled plans for naval drills involving more than 140 warships and more than 60 aircraft, seen as a show of strength.
The same day, the US warned that Russian intelligence officers have been recruiting current and former Ukrainian government officials to step in as a provisional government and cooperate with an occupying Russian force in the event of an invasion.
The US Treasury Department imposed sanctions on two current Ukrainian members of parliament and two former government officials accused of being part of the plot.
How unified are the US and its allies?
President Biden was heavily criticised for comments he made on Wednesday, when he bleakly predicted that Russia “will move in” on Ukraine, but appeared to suggest a “minor incursion” could attract a weaker response from the US and its allies.
The message provoked a rebuke from Ukrainian President Volodymyr Zelensky, who tweeted: “There are no minor incursions. Just as there are no minor casualties and little grief from the loss of loved ones.”
Mr Biden sought to clear up the confusion – and apparent disconnect with Mr Blinken’s tougher line – by saying any Russian troop movement across Ukraine’s border would qualify as an invasion and that Moscow would “pay a heavy price”.
Several European nations have urged Russia to change tack.
Speaking alongside Mr Blinken, Germany’s new Foreign Minister Annalena Baerbock pledged immediate action against any Russian invasion and did not rule out imposing measures that “could have economic consequences for ourselves”.
The UK’s Foreign Secretary Liz Truss has also called on Mr Putin to “desist and step back from Ukraine before he makes a massive strategic mistake” that would lead to terrible loss of life.
In a speech on Friday in Sydney, she urged Western powers to “step up” and warned that autocratic nations were being “emboldened in a way we haven’t seen since the cold war”.
Earlier this week, Britain announced it was supplying Ukraine with extra troops for training and defensive weapons.
Mr Biden is facing increasing calls from across the US political spectrum to take pre-emptive action against Russia.
Senior Republican Senator Lindsey Graham has called for “sanctions against Putin now”, while the Democratic Senator Richard Blumenthal has urged administration officials to begin “a massive airlift of … lethal weapons” to Ukrainian forces.
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