A massive truck bomb exploded near a Shiite mosque in the centre of the Iraqi capital on Tuesday, killing more than 75 people, security and hospital officials said.
The bomb ripped through the capital as 10,000 US and Iraqi troops launched a major air and ground assault on Al-Qaeda strongholds in the restive Diyala province, the biggest such operation seen in the violence-ridden area.
The explosion, the deadliest in Iraq since mid-April and the latest in a wave of tit-for-tat attacks against Sunni and Shiite mosques, spared the green dome of Al-Kholani mosque in the Sinak area but destroyed its main prayer hall.
Security officials said at least 61 people were killed and 130 others wounded, evacuated to five separate hospitals. The blast left a crater measuring six-metres (20-feet) by three metres, an AFP journalist said.
Police and volunteers pulled burning bodies out of cars while others dug through the pile of rubble to try to find survivors, according to the correspondent at the scene.
Groups of women wailed in the gray dusty air, while others chanted that the explosion was the work of those who blew up a revered Shiite shrine in the northern city of Samarra last Wednesday.
The explosion came just two days after the lifting of a citywide curfew intended to prevent a wave of sectarian Sunni-Shiite bloodletting following the Samarra bombing.
Meanwhile, the US military said it had killed 22 alleged insurgents in what it dubbed Operation Arrowhead Ripper as US-led troops supported by helicopters and heavy fighting vehicles poured into Diyala's provincial capital Baquba.
"Task Force Lightning commenced Operation Arrowhead Ripper today in a large-scale effort to eliminate Al-Qaeda in Iraq terrorists operating in Baquba and its surrounding areas," a military statement statement.
"Approximately 10,000 soldiers, with a full complement of attack helicopters, close air support, Strykers and Bradley Fighting Vehicles, are taking part in Arrowhead Ripper, which is still in its opening stages."
The military said the assault was launched with a rapid night-time air assault and that by daybreak 22 militants had been killed and two detained.
"The end state is to destroy the Al-Qaeda influences in this province and eliminate their threat against the people," said US Brigadier General Mick Bednarek.
Troops burst into several areas surrounding the western part of Baquba and were throwing up barriers across main entrances as helicopters swirled overhead, residents said.
Iraqi army Colonel Naguib al-Salahi said several civilians were feared killed or wounded. He did not have a precise number because "armed forces are preventing ambulances from entering the area."
In the town of Hibhib, north of Baquba, six Kurdish soldiers in the Iraqi army were killed in overnight clashes, Major General Anwar Mohammed Amin said.
Authorities imposed a curfew in Baquba as intense fighting broke out, with police fanning out across the city and using loudspeakers to warn people to stay indoors.
"We have begun a security plan and we will remove the armed men and the militias. We are here to help you," they announced.
As US-led troops have pressed on with a four-month surge of troops into Baghdad, insurgents have fanned off into surrounding areas, especially the farmsteads and orange groves of Diyala.
In recent months the province has become an arena of fighting between US-led forces, Shiite militias, and Sunni insurgents. Thousands of civilians have been killed and many thousands more have fled.
Nurtured by both the Tigris and Diyala rivers, Diyala contrasts with the arid provinces around it. The province is known as "mini-Iraq" for its ethnic and religious mix, and in recent months has erupted into a sectarian quagmire.
In the south, fierce clashes between security forces and Shiite militiamen in and around the southern cities of Amara and Nasiriyah since Monday killed at least 50 people.
At least 20 militants were killed in clashes around Amara, the military said, while 30 more people died and more than 90 were wounded in Nasiriyah, the city's police chief said.
The US military said another soldier was killed on Monday in eastern Baghdad, bringing to 3,520 the total US losses since the March 2003 invasion, according to an AFP count based on Pentagon figures.