The US said on Thursday that it has not questioned Russia about two American citizens who went missing after fighting Russian forces in Ukraine, and that there are allegations of a third missing American.

“As of today, we have not raised this with the Russian Federation… (We) haven’t seen anything from the Russians indicating that two such persons are in their possession,” US State Department spokesman Ned Price told reporters.

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.

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,” Price added, saying the third American was identified as missing in recent weeks.