PLEASE NOTE: EDIT CONTAINS MATERIAL THAT WAS ORIGINALLY 4:3

ROUGH CUT - NO REPORTER NARRATION

Two bombs concealed in air conditioning units inside a Sunni mosque south of the Iraqi city of Samarra exploded during Friday (September 20) prayers, killing at least 15 people, police and hospital sources said.

It was not immediately clear who was behind the attack, which took place in al-Mafraq, around 10 km (6 miles) south of Samarra.

At least 17 people were wounded, the sources said.

Iraq's delicate sectarian balance has come under growing strain from the civil war in neighbouring Syria, where mainly Sunni rebels are fighting to overthrow a leader backed by Shi'ite Iran.

Both Sunnis and Shi'ites have crossed into Syria from Iraq to fight on opposite sides of the conflict.

Al Qaeda's Syrian and Iraqi branches merged earlier this year to form the Islamic State of Iraq and the Levant, which has claimed responsibility for attacks on both sides of the border.

Iraq has also witnessed several incidents in recent weeks suggesting that Shi'ite militias, which have so far refrained from retaliating to attacks by Sunni insurgents, may once again be resorting to violence.