Turkish President Recep Tayyip Erdogan said on Wednesday his country had arrested one of the wives of Islamic State leader Abu Bakr al-Baghdadi, more than a week after he was killed during a raid by US special forces in Syria.

"The United States said Baghdadi killed himself in a tunnel," Erdogan said in his speech at the Republican Palace at a ceremony marking the 70th anniversary of the founding of the Faculty of Theology at Ankara University. We are making a fuss about it like them. Also, we arrested his sister and brother-in-law in Syria, "he said, without giving further details.

Baghdadi's death coincided with Turkey's military operation against Kurdish factions, which were a key ally of the West in the fight against the Islamic State, but Ankara considers Kurdish forces "terrorist".

A senior Turkish official said this week that Turkey had arrested Baghdadi's sister, husband and daughter and hoped to get information from them about IS, but Ankara did not specify whether they had information about ISIS operations.

Baghdadi emerged as a self-proclaimed "caliph" of Muslims, taking control of large swathes of Iraq and Syria between 2014 and 2017, and then a US-led coalition took away areas previously controlled by the group.

World leaders welcomed his death but warned they and security experts that the group remained a security threat in Syria and abroad.

US Secretary of State Mike Pompeo said two wives of Baghdadi were also killed at the site of the raid last month.

The group announced the appointment of a successor to Baghdadi named "Abu Ibrahim al-Hashimi al-Qurashi," and a senior US official said last week that Washington was trying to identify the identity of the new leader of the organization.