Two Americans fighting alongside Ukrainian forces north of Kharkiv in Ukraine have been missing for nearly a week and there are fears that they may have been captured by Russian forces, according to their families and a fellow fighter.

The men are Alexander John-Robert Drueke, age 39, from Tuscaloosa, Alabama, and Andy Tai Ngoc Huynh, age 27, from Hartselle, Alabama.

A man who wished to remain nameless for security reasons, who is acting as the team’s sergeant, provided CNN with photos of both men’s passports and their entry stamps into Ukraine.

The man said their unit was fighting under the command of Ukraine’s 92nd mechanized brigade on June 9, near the town of Izbytske.

He said Drueke and Huynh went missing during the battle, and subsequent search missions failed to find any remains. A post the following day on a Russian propaganda channel on Telegram claimed that two Americans had been captured near Kharkiv.

Bunny Drueke, Alex’s mother, told CNN that “they are presumed to be prisoners of war, but that has not been confirmed.” She said the US Embassy to Ukraine has not been able to verify whether her son has been captured.

Joy Black, Huynh’s fiancé, age 21, told CNN: “We don’t want to make assumptions about what might have happened at this time. Obviously, they’re looking at several scenarios. And one of them is that they might have been captured. But we don’t have absolute confirmation of that at this time.”

What the US is saying: A State Department spokesperson Wednesday said they “are aware of unconfirmed reports of two US citizens captured in Ukraine.”

“We are closely monitoring the situation and are in contact with Ukrainian authorities,” the spokesperson said. “Due to privacy considerations, we have no further comment.”

CNN’s Jennifer Hansler contributed reporting to this post.