Washington CNN  — 

The US-backed Syrian Democratic Forces have captured an individual the US assesses to be Mohammed Haydar Zammar, a Syrian-born German national linked to the 9/11 terrorist attacks.

“We can confirm that Mohammad Haydar Zammar, a Syrian-born German national, was captured more than a month ago by SDF partners as part of their ongoing operations to defeat ISIS inside Syria,” Pentagon spokesman Eric Pahon told CNN.

Pahon said Zammar “was captured during a unilateral operation conducted by the Syrian Democratic Forces.”

“We are working with our SDF partners to obtain additional details,” he added, calling Zammar’s capture “a strong reminder of the threat posed by ISIS and its network of foreign terrorist fighters.”

The spokesman for the People’s Protection Unit (YPG), Nouri Mahmoud, and the spokesman for the Syrian Democratic Forces, Mostafa Bari, refused to comment when contacted by CNN.

Zammar is believed to have recruited some of the perpetrators of the September 11, 2001, terror attacks on the United States, including hijacker Mohammed Atta. The 9/11 Commission report by the US government said Zammar reportedly took credit for influencing the Hamburg group, which Atta was a part of.

Zammar was arrested in Morocco in December 2001 and sent to Syria, where he was convicted of being a member of the Muslim Brotherhood. He was released from prison after the start of the uprising.

AFP was first to report Zammar’s capture, citing a Syrian Democratic Forces commander.

Gen. Joseph Votel, the head of US Central Command, which oversees US forces in the region, told Congress last month that the Syrian Democratic Forces currently hold approximately 400 foreign terrorist fighters.

“We are working with our partners in the government here to work to get them back to their countries so they can be prosecuted in accordance with their laws,” Votel said.

Votel added that the US was “working on improving the capacity of the Syrian Democratic Forces” to detain these foreign fighters for the long term in the event that some are not returned to their countries of origin.

CNN’s Tim Lister and journalist Mohammed Hassan in Northern Syria contributed to this report.