The Russian buildup has caused growing concern in the West in recent days, with the United States saying that troop levels are at their highest since 2014, when war first broke out with Moscow-backed separatists.

Asked by a US House of Representatives committee on the recent increase in tensions between the neighbors, General Tod Wolters said it was a "great concern."

But when a lawmaker asked him to evaluate the probability of a Russian invasion of Ukraine in the next few weeks, Wolters said it was "low to medium."

"My sense is that with the trend that I see right now, that the likelihood of an occurrence will start to wane," said the head of US European Command, which also commands NATO's allied forces.

For several weeks, clashes have increased between Kiev and pro-Russian separatists in eastern Ukraine, while tens of thousands of Russian troops have been deployed nearby, raising fears of a major military operation.

The Ukrainian government is also worried that Moscow is seeking to provoke a situation that would justify an armed operation.

Western countries have warned Moscow against displays of force, and Ukrainian President Volodymyr Zelensky will meet his French counterpart, Emmanuel Macron, in Paris on Friday.

Germany's Chancellor Angela Merkel will participate in the talks via videoconference.