A line of US military vehicles in Syria's northern city of Manbij. Image Credit: AFP

Beirut: "Dear Director, I am looking to get a position teaching English to students in the Islamic State."

So began Warren Christopher Clark, a substitute teacher from Texas, in a cover letter written sometime after 2014 and later obtained by American researchers studying extremism.

Clark wound up joining the extremist group in its Iraqi capital of Mosul under the nom de guerre Abu Mohammad Ameriki,  "The father of Mohammad the American."

Kurdish forces in Syria said Sunday that they had captured two American citizens hiding out in the country's final Daesh stronghold.

In a statement, the Syrian Democratic Forces, or SDF, identified the detainees as Warren Christopher Clark, 34, and Zaid Abed Al Hamid, 35. It said the pair had been captured alongside three others suspected of being foreign recruits in the extremist group.

Clark, 34, converted to Islam in 2004, according to local news reports. He graduated in 2008 from the University of Houston with a bachelor's degree in political science and a minor in global business, then worked as a substitute teacher in Texas before teaching English in Saudi Arabia and Turkey.

Law enforcement agencies say several dozen Americans joined Daesh in its once-sweeping self-proclaimed caliphate across Syria and Iraq. The SDF did not provide additional information about the two Americans it detained, but according to a report by George Washington University's program on extremism, Clark had sought work with Daesh and sent a resume and cover letter for an English-teaching job at the University of Mosul in Iraq.

"I have a long background in teaching a variety of different subjects . . . this has given me leadership skills and I have learned to adapt to new situations and environments with ease," Clark wrote in the cover letter, using his nom de guerre, Abu Muhammad Al Ameriki.

"Teaching has given me the opportunity to work with people from diverse cultural backgrounds and learning capabilities," he wrote.

The cover letter was found in a Mosul home after the Iraqi government regained control of the city in 2017 - three years after the militants seized it and a large swath of Iraq and Syria - and was published by the Program on Extremism at George Washington University in a lengthy report last year on 64 Americans who had joined Islamic State.

The US-led coalition did not immediately respond to a request for comment about the pair's detention, and spokesmen for the SDF provided no further details of their incarceration.

The men's fate could be complicated as Washington has shown little desire to extradite captives accused of being part of Daesh.

If sent back to the US, he and Clark would be the 15th and 16th Americans known to have returned home after joining Daesh, according to Seamus Hughes, the deputy director of the George Washington program.

Though Clark had applied to be an English teacher, it is unclear if that was his job for the terrorist group. In any case, he is likely to face terrorism charges if prosecuted in the U.S. The average prison sentence for the militants sent back to the US is 10 years, according to the report on the returnees.

He reportedly converted to Islam in 2004 and later became radicalized online, according to the deputy director of the George Washington program, who spoke to NBC about Clark early last year.

The NBC report described Clark as having come from a "middle-class church going family with ties to the military," citing someone who knew him in high school.

There was little publicly available information about Hamid.