ISIS releases audio message purportedly from leader Abu Bakr al-Baghdadi

ISIS on Thursday released an audio message purportedly from its leader, Abu Bakr al-Baghdadi, who has not been seen or heard from in months.

The audio message posted on militant websites features a voice that sounds like al-Baghdadi's exhorting all Muslims to take up arms and fight on behalf of the group's self-styled caliphate. The speaker references the Saudi-led air campaign against Shia rebels in Yemen, which began on March 26, and harshly criticizes the Saudi royal family.

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"Islam was never a religion of peace. Islam is the religion of fighting," he said. "No one should believe that the war that we are waging is the war of the Islamic State. It is the war of all Muslims, but the Islamic State is spearheading it. It is the war of Muslims against infidels."

"O Muslims go to war everywhere. It is the duty of every Muslim," the speaker said.

It was not immediately possible to verify whether the voice was al-Baghdadi's.

The last audio message purportedly from al-Baghdadi came in November, days after Iraqi officials said he was wounded in an airstrike on an Iraqi town near the Syrian border.

Al-Baghdadi has only appeared in public once, in a video showing him delivering a Friday sermon in the northern Iraqi city of Mosul last July, shortly after it was captured by his group.

In the latest message, al-Baghdadi blasted Arab rulers, calling them "guarding dogs" and saying the Yemen war will lead to the end of the Saudi royal family's rule.