The Islamic State group has 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.

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