Rex Tillerson
Rex TillersonReuters

United States Secretary of State Rex Tillerson said on Wednesday that the death of Islamic State (ISIS) leader Abu Bakr al-Baghdadi is only a matter of time.

"Nearly all of Abu Bakr Baghdadi's deputies are now dead, including the mastermind behind the attacks in Brussels, Paris and elsewhere," Tillerson told a coalition meeting in Washington, according to the AFP news agency.

"It is only a matter of time before Baghdadi himself meets this same fate," he added, speaking during a meeting of the 69 members of the U.S.-led military coalition fighting ISIS.

Baghdadi was believed to have been in Mosul, ISIS’s de facto capital, though a U.S. defense official told reporters earlier this month that he had fled the city.

There have been several reports in recent months suggesting that Baghdadi had been injured or even killed in coalition airstrikes, but none of those reports have been confirmed.

He refuted those reports by releasing an audio message in which he said he is "confident of victory" and called on the people of Mosul to fight the "enemies of God".

The northern city has been encircled and partially liberated by U.S.-backed Iraqi forces, and officials now think Baghdadi has been cut off from command.

"The great commonality among we who have gathered today is a commitment to bringing down a global force of evil and I emphasize the word commitment," Tillerson said on Wednesday, adding, "The success of our mission depends on a continued devotion to our stated objective of defeating this terrorist organization."