By Phil Stewart and Idrees Ali

WASHINGTON (Reuters) -There is a “low to medium” risk that Russia will invade Ukraine over the next few weeks, the top U.S. general in Europe said on Thursday, in the first such military assessment amid mounting concern about Russian troop movements toward Ukraine’s borders.

Air Force General Tod Wolters declined to explain the intelligence driving his assessment, which does not suggest the U.S. military expects a Russian invasion at this point, but is not ruling one out or playing down the risk.

But Wolters later suggested his view about the risks in the coming weeks and months was at least partly based on the disposition of Russian forces.

The Pentagon has declined to detail its assessment on the size and composition of those troops, referring reporters to Moscow. However, the White House disclosed that Russia has more troops on Ukraine’s eastern border than at any time since 2014, when it annexed Crimea and backed separatist territory seizures.

Asked by a lawmaker to estimate the chances of an invasion in the next few weeks, Wolters said: “Low to medium.”

Pressed by a different lawmaker to explain whether that risk would change after that period, Wolters kept his cards close, saying: “The answer is, it depends.”

“And I would have to take each and every second of the day from this point till tomorrow to give you a different answer,” he said.

If the current trajectory stayed the same, however, Wolters estimated the risk of an invasion could decrease.

“My sense is, with the trend that I see right now, that the likelihood of an occurrence will start to wane,” he said.

Ukraine and Russia have traded blame over a spike in violence in the conflict in eastern Ukraine, where Ukrainian troops have battled Russian-backed forces in a conflict that Kyiv says has killed 14,000 people since 2014.

Tensions over a buildup of Russian troops on Ukraine’s eastern border have pushed up the cost of raising domestic debt and prompted the government to accelerate efforts to secure more International Monetary Fund loans, a presidential adviser told Reuters on Thursday.

(Reporting by Phil Stewart and Idrees Ali; Editing by Franklin Paul and Jonathan Oatis)