The United States said on Thursday that Iranian military trainers were in Crimea helping Russian forces operate Iranian-made drones to attack targets in Ukraine, adding an alarming strand to a war that has heightened geopolitical tensions.

“We can confirm that Russian military personnel based in Crimea have been piloting Iranian UAVs and using them to conduct kinetic strikes across Ukraine, including in strikes against Kyiv in recent days,” U.S. State Department spokesman Ned Price told a daily briefing with reporters, referring to unmanned aerial vehicles, or drones. “We assess that ... Iranian military personnel were on the ground in Crimea and assisted Russia in these operations,” Price said. He said “we do have credible information” but he did not provide evidence.