The African Union (AU) expressed grave concern on Friday after Israel struck some 100 targets in Iran, including Tehran's nuclear and military sites.

The Chairperson of the African Union Commission Mahmoud Ali Youssouf, "expresses grave concern over reports of an Israeli airstrike on Iran and the ensuing escalation of hostilities in the Middle East," it said in a statement.

"The Chairperson calls for the immediate cessation of hostilities and urges all parties to exercise maximum restraint. He pointed out that the current developments pose a serious threat to international peace and security," it added.

The strikes early Friday set off explosions in Iran’s capital, Tehran. as Israel said it was targeting Iranian nuclear and military facilities. Iranian state media reported that the leader of Iran’s Revolutionary Guard Corps and at least four top nuclear scientists had been killed.

Israel's attack comes as tensions have escalated over Iran’s rapidly advancing nuclear program, which Israel sees as a threat to its existence.

Iran long has said its program is peaceful and US intelligence agencies have assessed Iran was not actively building a weapon.