The United States is warning that war could begin in Ukraine as soon as Wednesday, as Russia prepares its invasion.

Moscow has repeatedly disputed Washington’s version of events, saying it has massed more than 100,000 troops near the Ukrainian border to maintain its own security against aggression by NATO allies.

U.S. Secretary of State Antony Blinken expressed hope that Putin would choose diplomacy but said Washington would impose swift economic sanctions if Moscow invades.

“I continue to hope that he will not choose the path of renewed aggression and he’ll chose the path of diplomacy and dialogue,” Blinken told reporters after a meeting with Pacific leaders in Fiji. “But if he doesn’t, we’re prepared.”

Australia and New Zealand have joined the countries urging their citizens to leave Ukraine, after Washington said a Russian invasion, including a possible air assault, could occur anytime.

Putin, jostling for influence in post-Cold War Europe, is seeking security guarantees from Biden to block Kyiv’s entry into NATO and missile deployments near Russia’s borders.

Washington regards many of the proposals as non-starters but has pushed the Kremlin to discuss them jointly with Washington and its European allies.

Two calls in December between Biden and Putin produced no breakthroughs but set the stage for diplomacy between their aides.

Four-way talks in Berlin between Russia, Ukraine, Germany and France on Thursday made no progress.

THE THREAT IS GROWING

U.S. intelligence believes a rapid assault on Kyiv is possible and that Putin could order an invasion before the Winter Olympics end on Feb. 20,

On Twitter, Russia’s Deputy U.N. Ambassador Dmitry Polyanskiy accused Washington of fanning “hysteria” and mounting a “panic campaign.”

Ahead of the talks with Putin, Biden spoke about the crisis with the leaders of Britain, Canada, France, Germany, Poland and Romania, as well as the heads of NATO and the EU.

U.S. Secretary of State Antony Blinken also spoke with Ukraine’s foreign minister, Dmytro Kuleba.

“Our support for Ukraine’s sovereignty and territorial integrity is unwavering,” Blinken said after the call on Friday.

Washington also expressed concern that Russia and China were cooperating at the highest level, with a senior administration official saying on Saturday the two were “working to undermine us.”