A video posted online purports to show the leader of the Islamic State extremist group that has overrun much of Syria and Iraq delivering a sermon at a mosque in Iraq.

Iraqi forces have stormed a settlement of Iranian exiles near the two nations’ border that prime minister Nouri al-Maliki has long sought to expel.

Shiite cleric Muqtada al-Sadr issued a “final warning” to the Iraqi government to halt the US-Iraqi crackdown against his followers or he would declare “open war until liberation”.