Kurdish-led forces allied with the United States provided information — including used underwear for a DNA analysis — that was key to the operation that killed the Islamic State group's leader Abu Bakr al-Baghdadi, the leader of the Kurdish forces in Syria said Monday.

In an interview with NBC News, Gen. Mazloum Abdi of the Syrian Democratic Forces said his intelligence service had a source deep in al-Baghdadi's inner circle who described a room-by-room layout of the terror leader's compound on the Turkish border, including the number of guards, floor plan and tunnels.

Kurdish intelligence operatives who managed the source passed that information to American forces, giving U.S. Special Ops a better understanding of al-Baghdadi's safe house before striking it, according to Abdi.

Abdi said the unidentified source was on location during the raid and left with the attacking U.S. forces.

The source, whom Abdi described as one of al-Baghdadi's security advisers, proved to U.S. intelligence that he had direct access to al-Baghdadi this summer by turning over the ISIS leader's used underwear and later a sample of his blood.

U.S. intelligence tested those samples and got positive DNA matches for al-Baghdadi, kicking the hunt into high gear. The informant stole the underwear about three months ago and the blood sample was taken roughly one month ago, a Kurdish official said.

President Donald Trump thanked Syrian Kurds on Sunday for their role in the U.S. operation.

In an address to the nation live from the White House, Trump said the Kurds did not play a military role in the "dangerous and daring" raid, but provided "some information that turned out to be helpful."

For many Kurdish people, the brief acknowledgment — coming after Trump thanked Russia and other nations — did not sufficiently recognize their role in the raid, as well as the 11,000 men and women the Kurdish-led forces have lost in the almost five-year fight against ISIS.

The perceived lack of recognition only adds to hardening feelings among Kurds in northern Syria, furious over Trump's decision to withdraw, a move that critics see as a betrayal of the longtime U.S. allies and one that cleared the way for Turkey's incursion in the region.

Abdi nonetheless praised the raid early Sunday, adding that there was "joint intel cooperation on the ground and accurate monitoring" for five months.

"Thanks to everybody who participate in this great mission," he said on Twitter, tagging Trump in the post.

Trump said al-Baghdadi killed himself and three of his children, detonating a suicide vest as U.S. forces closed in on the compound in northwestern Syria.

He also acknowledged other nations he claimed played a part in the operation, including Russia, Turkey, Syria and Iraq.

The Syrian Democratic Forces are led by the Kurdish People's Protection Units (YPG), which has long angered the Turkish government. Turkey views the YPG an extension of the separatist Kurdistan Workers' Party, which is considered a terrorist group by Turkey and the United States.