Islamic State tape said to be of Abu Bakr al-Baghdadi, leader reported killed

Islamic State has released a defiant audio recording it said was of chief Abu Bakr al-Baghdadi, after air strikes on jihadist leaders in Iraq sparked rumours he had been wounded or killed.

In the 17-minute message released on Thursday, the man purported to be Baghdadi vowed that Islamic State, which has overrun swathes of Iraq and Syria, would continue to expand despite international air strikes, and that its opponents would be drawn into a ground war.

"Be assured, Oh Muslims, for your state is good and in the best condition. Its march will not stop and it will continue to expand," said the man in the recording, whose voice sounded like Baghdadi's.

"Soon, the Jews and Crusaders will be forced to come down to the ground and send their ground forces to their deaths and destruction," he said.

US President Barack Obama has announced plans to double the number of US military personnel in Iraq to 3,100 to help advise and train Baghdad's forces - a move the man in the recording said was the start of the ground war between the two sides.

The message was the first said to be from Baghdadi since a video released in July of him delivering a sermon in the northern Iraqi city of Mosul.