Turkey ‘captures sister of killed ISIS leader’ Abu Bakr al-Baghdadi

(Department of Defence/AP)

Turkey has captured the older sister of the killed leader of the so-called Islamic State group in north-western Syria, a senior official said, calling the arrest an intelligence “gold mine”.

Little is known about the sister of Abu Bakr al-Baghdadi.

The Turkish official said the 65-year-old known as Rasmiya Awad was captured in a raid on Monday on a trailer container she was living in with her family near the town of Azaz.

The area is part of the region administered by Turkey.

The official said the sister was with her husband, daughter-in-law and five children. The adults are being interrogated, he said.

Al-Baghdadi was killed in a US raid in the nearby province of Idlib last month.

The US Defence Department released footage of the raid. Credit: AP

"This kind of thing is an intelligence gold mine. What she knows about (IS) can significantly expand our understanding of the group and help us catch more bad guys," the official said.

Al-Baghdadi, an Iraqi from Samarra, was killed in a U.S. raid in the nearby province of Idlib last month.

The raid was a major blow to the group, which has lost territories it held in Syria and Iraq in a series of military defeats by the U.S-led coalition and Syrian and Iraqi allies.

Many IS members have escaped through smuggling routes to northwestern Syria in the final days of battle ahead of the group's territorial defeat earlier this year, while others have melted into the desert in Syria or Iraq.

The reclusive leader al-Baghdadi was known to be close to one of his brothers, known by his nom de guerre Abu Hamza.

Al-Baghdadi's aide, a Saudi, was killed hours after the raid, also in northwestern Syria, in a US strike.

The group named a successor to al-Baghdadi days later, but little is known about him or how the group's structure has been affected by the successive blows.