The Islamic State group released a defiant audio recording Thursday 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, the man purported to be Baghdadi vowed that IS, which has overrun swathes of Iraq and Syria, will continue to expand despite international air strikes, and that its opponents will be drawn into a ground war.

"Be assured, O 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 but whose identity could not be independently confirmed.

"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 up to 3,100 to help advise and train Baghdad's forces -- a move the man in the audio 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, shortly after IS proclaimed a "caliphate" over parts of Iraq and Syria, of the jihadist leader delivering a Friday sermon in the northern Iraqi city of Mosul.

While the recording seemed aimed at dispelling speculation that Baghdadi was seriously injured or dead, it did not mention the strikes against IS leaders.

But it did reference the decision by Ansar Beit al-Maqdis, Egypt's deadliest militant group, to pledge allegiance to Baghdadi and IS, which was announced after the strikes.

- Strikes sparked rumours of demise -

The United States said that coalition aircraft launched strikes targeting IS leaders in the area of their northern hub of Mosul on Friday, setting off a flurry of speculation that Baghdadi was wounded or killed.

Some reports meanwhile pointed to another alleged strike near Iraq's border with Syria, saying Baghdadi was hit there instead.

But officials in both Iraq and the United States have made clear that no one is yet certain about Baghdadi's fate.

Pentagon spokesman Colonel Steven Warren said Monday that "the bottom line from our perspective is we simply cannot confirm his current status."

And senior Iraqi officials from the interior and defence ministries and the intelligence service said investigations were ongoing.

The death of the elusive IS leader would be a major victory for the US-led coalition, but with both areas where strikes were rumoured to have hit Baghdadi far from government control, confirming anything there will be difficult if not impossible.

Rumours of Baghdadi's demise have surfaced before and the absence of video in Thursday's release by the IS group's media arm is likely to fuel further speculation he was indeed wounded.

IS spearheaded a militant offensive in June that overran Iraq's second city Mosul and then swept through much of the country's Sunni Arab heartland, adding chunks of a second country to territory it already held in Syria.

It has carried out atrocities in both countries.

The group has killed hundreds of Iraqi and Syrian tribesmen who opposed it, attacked members of the Yazidi and other minorities, sold women as slaves, executed scores of Iraqi security personnel and beheaded Western journalists and aid workers on camera.

IS is one of the most powerful forces in Syria's civil war, a blood-soaked conflict that, combined with former Iraqi premier Nuri al-Maliki's divisive policies, facilitated the group's rise.

Activists and a monitoring group said Thursday that United Nations aid has reached the last rebel-held area in the central Syrian city of Homs for the first time in six months.

"On Tuesday and Wednesday, 30 trucks of aid arrived in Waer for the first time in six months," Rami Abdel Rahman of the Syrian Observatory of Human Rights told AFP.

IS meanwhile claimed responsibility on Thursday for a suicide bombing targeting police in Iraq the day before, saying it had been carried out by a Dutch national.

It is the second attack allegedly involving a suicide bomber from a Western country in less than a week, after a British national blew up a truck packed with explosives in a northern town on Friday.

In Arbil, the capital of Iraq's region of Kurdistan, a breakthrough was reached Thursday between the autonomous local government and the federal authorities on a long-standing budget dispute.

The Kurdistan Regional Government said a deal had been struck whereby Baghdad would transfer half a billion dollars of frozen payments for the salaries of Kurdish civil servants in exchange for 150,000 barrels per day of Kurdish oil.

A resolution of the dispute was seen as key to improving cooperation between Arbil and Baghdad in their common fight against IS.