Grand Mufti Abdul Aziz Al-Asheikh has urged Muslims to confront the "oppressive" Islamic State jihadists if they fight Muslims after seizing swaths of Iraq and Syria.
"This group is aggressive and oppressive. It sheds blood," Aleqtesadiah daily quoted Al-Asheikh as saying.
"If they fight Muslims, then Muslims must fight them to rid people and religion of their evil and harm," he said in a response to a request from an Iraqi for a fatwa or edict on fighting IS.
"They have been killing ever since they began their fight. Their killing is filled with mutilations and hideousness that distort (the image of) Muslims," Al-Asheikh said.
His remarks come as the United States seeks to build a broad-based international coalition to fight the Islamic State, which has carved out a stronghold in large areas of Syria and Iraq.
The United States last month launched airstrikes against the militant group in Iraq, in support of government forces and allied tribesmen, as well as Kurdish Peshmerga fighters in the north.
Last month, the Kingdom's highest religious authority branded Al-Qaeda and IS jihadists Islam's "No. 1 enemy", and warned Muslim youth to steer clear of "calls for jihad" issued on "perverted" grounds.
IS jihadists, already well established in Syria, launched an offensive in Iraq on June 9 and rapidly seized control of vast swaths of territory there.