The United States said diplomacy could still resolve a standoff with Moscow over Ukraine but added that the risk of a Russian invasion was high enough to warrant pulling U.S. embassy staff out of Kyiv.

U.S. Secretary of State Antony Blinken was speaking after talks on Saturday with Japanese and South Korean counterparts, following Washington's warning that Russia's military, which has more than 100,000 troops massed near Ukraine, could invade at any moment. Moscow denies having any such plans.

A flurry of meetings and phone calls in recent days between top Western and Russian officials has produced no sign of a breakthrough to resolve in weeks of escalating tensions.

Germany Chancellor Olaf Scholz is set to meet Russian President Vladimir Putin on Tuesday but a German source said Berlin did not expect "concrete results" from those talks. 

Scholz would make clear the West was united and any aggression would prompt "painful, considerable sanctions" on Russia, the source said.

"The diplomatic path remains open. The way for Moscow to show that it wants to pursue that path is simple. It should de-escalate, rather than escalate," Blinken said after his meetings in the U.S. Pacific archipelago of Hawaii.

In an hour-long call on Saturday, U.S. President Joe Biden told Putin that the West would respond decisively to any invasion of Ukraine, adding such a step would produce widespread suffering and isolate Moscow.

Some airlines have canceled or diverted flights to Ukraine amid heightened fears that an invasion by Russia is imminent despite intensive weekend talks between the Kremlin and the West.

In an hourlong Saturday call with Russian President Vladimir Putin, President Joe Biden said that invading Ukraine would cause “widespread human suffering” and that the West was committed to diplomacy to end the crisis but “equally prepared for other scenarios,” the White House said. It offered no suggestion that the call diminished the threat of an imminent war in Europe.

The two presidents spoke a day after Biden’s national security adviser, Jake Sullivan, warned that U.S. intelligence shows a Russian invasion could begin within days.

Russia denies it intends to invade but has massed well over 100,000 troops near the Ukrainian border and has sent troops to exercises in neighboring Belarus. U.S. officials say Russia’s buildup of firepower has reached the point where it could invade on short notice.