(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.

That third person is believed to be U.S. Marine veteran Grady Kurpasi, his dad confirmed to NewsNation.

Grady Kurpasi Sr. fears his son has been captured by Russian forces. He said a “good source” told him his son’s cell phone was traced to a mall in Kherson, Ukraine that’s being used as a Russian prison.

His dad says that Grady always tried to help people and set things straight in areas having conflict. Grady was trying not to worry his dad, and told him he was going overseas to go on vacation and didn’t mention Ukraine. That was on March 7.

The elder Kurpasi hasn’t heard from his son since.

He believes his son went there to train Ukrainian troops, but agreed to go on one mission and was captured.

“I love you,” Kurpasi Sr. said on “NewsNation Prime.” “I believe in you. I want you home as soon as possible,”

Grady has had four deployments, including three to Iraq, and two of which he volunteered to go. His father says he has three Purple Heart awards.

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 also feared captured, family members have said. 

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.

Reuters contributed to this report.