The Islamic State of Iraq and the Levant (ISIL) has released an audio recording it says is of its leader, Abu Bakr al-Baghdadi, just days after targeted air strikes in Iraq led to rumours he had been wounded or killed.

In the 17-minute message, the man, purported to be Baghdadi, made no direct reference to the strike against ISIL's leadership, but made mention of a failed "crusade", without going into any specific details of the air raids or how they were failing.

He also mentioned developments that have occurred since the strikes, including Egypt's Ansar Beit al-Maqdis pledging its allegiance to ISIL.

This would place the recording posted on the web on Thursday as being made within the past 36-hours.

In the message, Baghdadi called for the fighting to continue, saying that the US and its allies feared the return of the Islamic Caliphate.

"Be assured, O Muslims, for your state is good and in the best condition," he said according to an English transcript of the message released together with the recording.

The US said coalition aircraft launched attacks targeting ISIL leaders near Mosul on Friday, setting off the speculation that Baghdadi had been wounded.

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

Timing significant

Al Jazeera's Imran Khan, reporting from Baghdad, said the timing of the audio recording's release was significant.

"Since Saturday, rumours have been swirling saying Baghdadi was injured or killed. ISIL has denied this," he said. 

"This will be used by ISIL as evidence of the failure of the US to get their leader, and indeed, that is what this audio tape is intended to imply."

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The audio message was the first from Baghdadi since a video was released in July, shortly after ISIL proclaimed a caliphate over parts of Iraq and Syria, of him delivering a Friday sermon in the northern Iraqi city of Mosul.

The voice in Thursday's audio document appeared to match the video, but there was no immediate confirmation of its authenticity from other sources.

In the recording, Baghdadi says that the US-led coalition of dozens of nations contributing to the military effort against ISIL is failing to defeat his group.

"Its march will not stop and it will continue to expand, by Allah's permission," he says.

"The march of the mujahideen will continue until they reach Rome.

"And soon, the Jews and Crusaders will be forced to come down to the ground and send their ground forces to their deaths and destruction."

Expanding influence

The recording makes specific calls for attacks against the rulers of Saudi Arabia, saying ISIL was expanding its influence within the kingdom.

Saudi Arabia has joined the US in carrying out air strikes against ISIL.

"O sons of al-Haramayn ... the serpent's head and the stronghold of the disease are there. ... Draw your swords and divorce life, because there should be no security for the Saloul," Baghdadi said, using a derogatory term to refer to the leadership of Saudi Arabia.

When asked about the tape, Jen Psaki, US State Department spokesperson, said she could not confirm it was Baghdadi.

"Clearly the brutality, rhetoric, efforts to incite by any leaders of ISIL is not a new phenomenon. It is a reminder to everyone in the region and around the world, what their intentions are," she said.

Source: Al Jazeera and agencies