At least 75 people have been killed and 130 wounded in a truck bomb blast in the Iraqi capital, Baghdad.
The explosion occurred close to the Shia al-Kholani mosque and caused one wall of the building to collapse.
The green dome of the mosque escaped damage in the bombing, but the main prayer hall was destroyed.
It is understood a parked truck was loaded with tanks of pressurised gas before being detonated.
The attack prompted exchanges of gunfire in the area and comes following a lull in violence due to a curfew imposed after the bombing of the al-Askari shrine in Samarra.
Meanwhile, the US military has launched one of the single biggest operations in Iraq since the end of the invasion in 2003.
The attack is focused on suspected militants north of Baghdad and involves over 10,000 troops.
The military said that 22 militants had been killed in the early hours of the offensive, which is taking place around the city of Baquba in Diyala province an 'al-Qaeda in Iraq' stronghold.
Attack helicopters and ground forces launched the offensive to 'eliminate' militants operating in Baquba and its surrounding areas.
US officials claim the group is trying to tip Iraq further into civil war, following a wave of car bomb attacks.
The operation comes just days after the US military said it had completed its troop build-up in Iraq, increasing the force to 160,000 soldiers.
Nearly 28,000 additional troops have been sent to Iraq, mainly to Baghdad but also to the western Anbar province. That campaign has prompted many militants to shift the focus of their attacks to other areas, especially Diyala province.
