Syrian Democratic Forces Warren Christopher Clark, 34, and Zaid Abed al-Hamid, 35, were among five men recently captured fighting for ISIS in Syria, according to the U.S-backed Syrian Democratic Forces.

Two Americans were reportedly captured fighting for the self-described Islamic State in Syria last week, the U.S-backed Syrian Democratic Forces said on Sunday.

One of the Americans was identified as 34-year-old Warren Christopher Clark, aka Abu Mohammad al-Ameriki, who formerly taught in Texas. The other was 35-year-old Zaid Abed al-Hamid, aka Abu Zaid al-Ameriki, according to the Syrian Democratic Forces.

They were reportedly captured with three other men, who were identified as Pakistani and Irish.

The U.S. government has not yet confirmed the report.

These terrorists were captured by our forces this week in a #Hajeen

Two Americans, two Pakistanis and one Irishman pic.twitter.com/eRIrpCcwXj — Mustafa Bali (@mustefa2bali) January 6, 2019

A Pentagon spokesman told CNN the report is under investigation.

“We are aware of open source reports of reportedly American citizens currently in custody who were believed to be fighting for ISIS,” Commander Sean Robertson said, adding the Pentagon is not yet able to confirm the information.

The Pentagon did not respond to a request for additional comment.

Clark is a graduate at the University Houston who sent his teaching resume to ISIS after becoming radicalized sometime around 2004, NBC News reported last year.

A copy of his resume and cover letter seeking a job as an English teacher were found in an Iraq neighborhood that had been taken over by ISIS fighters.

“I’m looking to get a position teaching English to students in the Islamic State. I was born and raised in the United States and have always loved teaching,” the cover letter read. “I have a long background in teaching a variety of different subjects and have instructed students of all ages at several schools.”

Prior to allegedly joining ISIS overseas, he was a substitute teacher from August of 2008 to November of 2010 in Fort Bend, Texas, a spokeswoman for the school district confirmed to HuffPost.

Details about al-Hamid are less clear. The New York Times suggested that al-Hamid may be Trinidadian or have dual U.S. citizenship. He was in a past ISIS video discussing life in Trinidad and was detained in 2011 for allegedly plotting to kill Trinidad’s prime minister, the Times reported.

Simon Cottee, a senior lecturer in criminology at the University of Kent who tracks ISIS, told the Times that Hamid joined the terrorist group in 2014 with his wife and three children.

If Clark and al-Hamid are returned to the U.S. to face charges they would be only the 15th and 16th Americans to do so after joining ISIS in Iraq and Syria, Seamus Hughes, a counterterrorism expert at George Washington University’s Program on Extremism, told the Times.

“To put it in context, the Brits are talking about hundreds of returnees,” Hughes said.