DIYARBAKIR, Turkey — Turkey has captured the older sister of Abu Bakr al-Baghdadi, the leader of the Islamic State who died in an American raid in northwestern Syria a week ago, a senior Turkish official said Tuesday.

Mr. al-Baghdadi’s sister, Rasmiya Awad, 65, was detained in the town of Azaz, in a Turkish-controlled region of northern Syria, where she was living with her husband and family members.

The capture of such a close relative — and one said to be affiliated with the Islamic State movement — might yield a trove of intelligence information, the official said.

In the years since he declared a caliphate in 2014, Mr. al-Baghdadi had become intensely security conscious. He trusted only his family and a close circle of associates, according to women who were held by him as sex slaves, as well as several senior aides interviewed after their capture in prison in Iraq.