A Syrian Kurd undercover agent took a pair of Abu Bakr al-Baghdadi’s underwear for DNA identification ahead of the US raid that killed the jihadist leader, a Kurdish official said on Monday.

Polat Can, a senior adviser to the Kurdish-led Syrian Democratic Forces (SDF), published details of the intelligence work that led to the US raid in which the founder of the Islamic State group was killed.

"Since 15 May, we have been working together with the CIA to track al-Baghdadi and monitor him closely," he said.

"Al-Baghdadi changed his places of residence very often," Polat Can said, adding that the asset managed to reach the house where the IS chief was believed to be hiding.

"Our own source, who had been able to reach al-Baghdadi, brought al-Baghdadi’s underwear to conduct a DNA test and make sure (100%) that the person in question was al-Baghdadi himself," the adviser wrote on Twitter.