Anti-ISIS forces in Syria have detained a Syrian-born German man suspected of recruiting some of the 9/11 hijackers to Al Qaeda, the Pentagon said Thursday.

Syrian Democratic Forces (SDF) captured the detainee, identified as Mohammed Haydar Zammar, more than a month ago, Pentagon spokesman Eric Pahon said.

Zammar, who is his mid-fifties, was apprehended in northern Syria and was being interrogated, a senior Kurdish commander told Agence France-Presse on Wednesday. Zammar's fate remained unclear. The SDF is a predominantly Kurdish network of fighters.

The jihadist is known for allegedly helping plan the Sept. 11, 2001, attacks in the U.S., including recruiting some of the hijackers to the terror group. As the Pentagon noted, the official 9/11 Commission Report described him as an "outspoken, flamboyant Islamist" who extolled "the virtues of violent jihad."

Zammar fled Germany after the attacks and relocated to Morocco, where he soon was arrested in an operation involving CIA agents.

He later was handed to Syrian authorities who, in 2007, sentenced him to 12 years in prison for being a member of the Muslim Brotherhood, according to German state broadcaster Deutsche Welle.

He was released from prison after the Syrian civil war broke out in the region and most hardline jihadists and Islamists were released. Zammar, among many others, was believed to have joined the Islamic State terror group.

The Kurdish official didn’t say if Zammar has been actively engaged in fighting for the terror group in Syria.

Fox News' Jennifer Griffin contributed to this report.