US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov are to hold talks in Geneva on Friday to discuss soaring tensions over Ukraine after a flurry of meetings between officials on both sides in the last week produced no breakthroughs.
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 also wants the Western defensive alliance to abandon military activity in eastern Europe, but has received no reassurances.