WASHINGTON

The State Department said Thursday that it is aware of reports suggesting a third American has been captured by Russia while fighting alongside Ukrainian forces.

"There are reports of one additional American whose whereabouts are unknown. I can't speak to the specifics of that case. Unfortunately, we don't know the full details of that case," spokesman Ned Price told reporters.

He acknowledged that the agency has spoken with "a family."

CNN reported Wednesday that Alexander John-Robert Drueke, 39, from Tuscaloosa, Alabama and Andy Tai Ngoc Huynh, 27, of Hartselle, Alabama, have been missing for nearly one week after fighting alongside Ukrainian forces in the country's northeast.

Russia has been pushing to capture the eastern region known as the Donbas since April after failing to take the capital, Kyiv, and pulling its forces from northern Ukraine.

Details on the third captured American are scarce other than Price's acknowledgment, but he continued to warn US nationals against traveling to Ukraine to take up arms against Russia.

"We continue to urge in every way we can American citizens not to travel to Ukraine because of the attendant dangers that is posed by Russia's ongoing aggression," said Price.

He said the US has not reached out to the Kremlin regarding the reported detainees but has spoken with the Ukrainian government, the International Committee of the Red Cross and "other partners," including the UK.

"As of today, we have not raised this yet with the Russian Federation. If we feel that such outreach through our embassy in Moscow or otherwise, would be productive in terms of finding out more information on the whereabouts of these individuals we won't hesitate to do that," he added.