Defense Secretary Mattis will ‘believe otherwise when we know we've killed him’

The Daesh terror group’s proclaimed "caliph" is likely still alive despite numerous claims of his death, Defense Secretary James Mattis said Friday.

"I think that he's alive, and I'll believe otherwise when we know we've killed him," Mattis told reporters. "But we're going after him."

Numerous claims have surfced of Abu Bakr al-Baghdadi’s death from monitors and countries, most notably Russia, that said last month it believed it killed him in an airstrike as he met senior Daesh leaders.

American officials had been reluctant to confirm or deny the claim, but Mattis' comments are the strongest yet against Moscow's assertion.