BAGHDAD, 21 June 2007 — Suspected Shiite militants blew up two Sunni mosques yesterday south of Baghdad, causing heavy damage but no casualties. The bombings were apparently revenge strikes for a suicide truck bombing a day before that badly damaged an important Shiite mosque in the heart of the capital. At least 87 died in that attack.

Thousands of US and Iraqi troops, meanwhile, pressed forward on the second day of an operation aimed at clearing a Sunni insurgent stronghold northeast of Baghdad. The US military said at least 30 Al-Qaeda fighters were killed and several bombs and weapons caches destroyed as the soldiers fought their way through the streets of Baqouba.

The US military operation that involves some 10,000 American soldiers in Diyala province, an Al-Qaeda bastion to the north and east of Baghdad, matched in size the force that American generals sent against the insurgent-held city of Fallujah 21/2 years ago.

Iraqi forces also have joined the battle in Diyala. Iraqi Defense Ministry spokesman Mohammed Al-Askari said about 5,000 Iraqi soldiers and 2,000 paramilitary police were fighting, while the military said about 1,000 Iraqi soldiers and an equal number of police were involved. The differing numbers could not be immediately reconciled.

In addition to the 30 Al-Qaeda fighters killed in the operation, Iraq’s Defense Ministry said that three civilians had been wounded, 13 suspected Al-Qaeda fighters were detained and 14 roadside bombs dismantled. Three car bombs also were defused and three weapons caches seized.

The head of a Sunni insurgent group that has turned against Al-Qaeda and is cooperating with US and Iraqi forces in the area said his fighters were participating in the operations and had succeeded in clearing several neighborhoods in eastern and western Baqouba.

The militant leader, who declined to be identified for fear of retribution, spoke as his fighters linked arms, chanted and danced while women ululated in celebration. An Associated Press reporter also saw residents in the Mustafa area in western Baqouba serving food to fighters who had battled Al-Qaeda and starting to repair their stores.

In Tuesday’s mosque bombings, police said suspected Shiite militiamen detonated a bomb inside a Sunni mosque in Haswa, 50 mm south of Baghdad, at about 1 a.m. About six hours later, militants struck again at mosque near Hillah, about 95 km south of the capital. Police spoke on condition of anonymity because they feared retribution.

The attackers near Hillah also targeted the imam’s house near the mosque, but the cleric fled when he saw them coming, according to the police. Tuesday’s suicide truck bombing against the Khulani mosque in central Baghdad was the deadliest single attack in Iraq since April 18, when at least 127 civilians were killed when a bomb detonated parked car at a mostly Shiite market in central Baghdad.

At a joint briefing with a US military spokesman, Iraqi Army spokesman Brig. Qassim Al-Mousawi said the truck was carrying about 50 cooking gas cylinders and about 500 kg of TNT. Asked how the suicide bomber managed to drive his truck bomb through Baghdad and next to the mosque, Al-Mousawi said that it was booby-trapped in the nearby industrial area of Sheik Omar. There were no checkpoints between there and the mosque, he said. Authorities are planning to put security fences near the mosques.

Police initially said the bomb was hidden in a truck piled high with electric fans and air conditioners. The US military spokesman, Rear Adm. Mark Fox, acknowledged “an increasing pattern of attacks” against the Green Zone, a day after a mortar barrage against the heavily fortified area sent soldiers and contractors scrambling for cover.

Militants fired a volley of mortars into the Green Zone, which houses the US and British embassies as well as Iraqi government houses on the west bank of the Tigris River, officials said Tuesday. The US Embassy said no casualties were reported, but the attack was the latest in what has become a nearly daily occurrence despite stringent security measures aimed at protecting the area.