BAGHDAD A major pilgrimage of hundreds of thousands of Iraqi Shi'ites to a Baghdad shrine passed peacefully on Tuesday, a day after three female suicide bombers killed 35 people among crowds of pilgrims.
Authorities lifted a vehicle curfew in the capital, imposed for the commemoration of the death of Imam al-Kadham, one of Shi'ite Islam's 12 imams.
"I congratulate the millions of people and the mourning processions which took place with the utmost organisation, showing great coordination with the armed forces," said a statement from Prime Minister Nuri al-Maliki's office.
Many pilgrims had appeared undeterred by Monday's attacks, which bore the hallmarks of Sunni Islamist al Qaeda. Black-clad Shi'ites from around Iraq packed Baghdad's streets as they made their way to the Kadhamiya shrine in the city's north.
Shi'ite pilgrims usually travel to such events on foot. Tents were set up along the way to hand out food and water.
Violence in Iraq has fallen to four-year lows, but the bombings underscored the challenge for Maliki, especially as U.S. troops draw down while his forces take on greater responsibility for safeguarding the country.
In the latest major crackdown on militants, Iraqi troops began a security operation in northeastern Diyala province, officials said. Al Qaeda has sought to stoke tensions in religiously mixed Diyala, close to Baghdad.
The government and U.S. officials condemned the blasts in Baghdad, as well as a suicide bombing in the northern city of Kirkuk on Monday that killed 23 people.
More than 250 people were wounded in the four attacks, making it one of the bloodiest days in Iraq this year.
The annual pilgrimage to the Kadhamiya shrine is one of the most important events in the Shi'ite religious calendar.
Security forces had put female guards around Kadhamiya to search women, but all Monday's blasts happened in central Baghdad, which many pilgrims passed through to reach the shrine.
Iraqi men are also reluctant to search women, prompting al Qaeda increasingly to use females who easily hide explosives under their flowing black robes.
U.S. commanders caution that, despite better security, suicide bombers wearing vests packed with explosives will still manage to slip into crowded places. Women have carried out more than 20 suicide attacks in Iraq this year.
In multi-ethnic Kirkuk, shops opened after a curfew imposed in the wake of Monday's was lifted, residents said.
Officials said the Diyala operation began with raids in the local capital Baquba, 65 km (40 miles) northeast of Baghdad.
Iraqi police and more than two Iraqi army divisions, which consist of up to 9,000 soldiers, are taking part.
The U.S. military has said the crackdown would be run by Iraqi forces with minimal U.S. involvement.
"The aim is to completely cleanse Diyala province. The Iraqi army will be executing this operation," said Major-General Abdul-Kareem al-Rubaie, commander of Diyala security operations.
Similar offensives in southern Iraq and Baghdad -- in areas that were once strongholds of Shi'ite cleric Moqtada al-Sadr's Mehdi Army militia -- have been largely successful.
Another big operation is also under way in the northern city of Mosul, once called al Qaeda's last major urban stronghold in Iraq. Residents there say they still fear the militant group.
The U.S. military commander in Iraq, General David Petraeus, told Reuters on Monday that Iraqi and U.S. forces now held virtually all of the country.
"I think it's accurate to say that Iraqi and coalition forces control the vast majority of the country. That is of course a major change from even just a year ago," Petraeus said.
Petraeus has repeatedly said recent security gains in Iraq are fragile and reversible.