The U.S. is raising the alarm with European Union allies that Russia may be weighing a potential invasion of Ukraine as tensions flare between Moscow and the bloc over migrants and energy supplies, writes Bloomberg.

With Washington closely monitoring a buildup of Russian forces near the Ukrainian border, U.S. officials have briefed EU counterparts on their concerns over a possible military operation, according to multiple people familiar with the matter.

The assessments are believed to be based on information the U.S. hasn’t yet shared with European governments, which would have to happen before any decision is made on a collective response, the people said. They’re backed up by publicly-available evidence, according to officials familiar with the administration’s thinking.

A White House official said Thursday evening that the U.S. was consulting with allies over the buildup, considered Ukraine a partner and denounced any and all aggressive acts by Russia.

Russia says military deployments on its territory are an internal matter and it denies any aggressive intentions, while accusing the U.S. of provocation by sailing warships in the Black Sea close to its territory this week.