(NewsNation) — The United States said on Thursday it was aware of reports that a third U.S. citizen is missing after traveling to Ukraine and it had not yet asked Russia about two Americans reportedly captured after going to the country to fight Russian forces.

“As of today, we have not raised this yet with the Russian Federation … (We) haven’t seen anything from the Russians indicating that two such individuals are in their custody,” U.S. State Department spokesman Ned Price told reporters, describing reports about the two men as unconfirmed.

According to reports, the third missing American has been identified as U.S. Marine veteran Grady Kurpasi. His wife said the last time that she heard from him was between April 23 and April 24.

A family friend of Kurpasi’s says his cellphone signal was recently traced to the vicinity of a large shopping mall in the southern part of Ukraine.

Alexander Drueke, 39, of Tuscaloosa, Alabama, and Andy Huynh, 27, of Hartselle, Alabama, went to Ukraine as volunteer fighters against Russian forces, have been missing for a week, and are feared captured, family members have said. 

The U.S. military said the two men had served in the U.S. armed forces in the past – Huynh for the Marine Corps and Drueke in the Army Reserves – but provided no information about their current whereabouts.

A disturbing new image now circulating on the social media app Telegram appears to show the men in the back of a military truck with their hands tied behind them. The U.S. Department of State has not been able to confirm this, but did say if the veterans were captured, they should be treated as prisoners of war.

The U.S. military has repeatedly denied U.S. troops are deployed to Ukraine and told veterans there are better ways to help Ukraine than answering calls from Kyiv to fight there.

Russia invaded Ukraine on Feb. 24, saying it was engaged in a “special military operation” to disarm and “denazify” its neighbor. Ukraine and its allies say Moscow has launched an unprovoked war of aggression, killing thousands of civilians.

Reports that the two had been taken as prisoners of war by Russia are unconfirmed, the families and U.S. officials have said. Earlier, the White House said it was “working very hard to learn more” about the two. 

“There are reports of one additional American whose whereabouts are unknown… Our understanding was that this individual had traveled to Ukraine to take up arms,” Price added, saying the third American was identified as missing in recent weeks.

The U.S. Department of State continues to urge American citizens not to travel to Ukraine.

Reuters contributed to this report.