The attack came as the hardline Shia cleric Moqtada al-Sadr declared three days of mourning to protest at parliament’s approval on Thursday of the accord, which will govern the presence of some 150,000 US troops across the country.

The blast ripped through the main mosque in the town of Musaib after the attacker, strapped with explosives, darted past guards and into the crowd of abut 300 worshippers inside, police Lieutenant Kadhim al-Shammari said.

One of those killed was an old woman begging for alms at the entrance to the mosque, he added. Another 15 people were wounded in the attack, which destroyed the building’s windows and doors and filled it with smoke.

It was unclear whether the attack was linked to the approval of the military pact or Sadr’s declaration of mourning, but the mosque’s congregation is considered loyal to the reclusive cleric, who is believed to be in Iran.

In July 2005 more than 70 people were killed at the same mosque when a suicide bomber detonated a truck loaded with explosives and cooking gas near the building.

Sadr issued a statement on Friday calling on his supporters to “put up black flags, organise mourning ceremonies across the country and hold peaceful demonstrations” to protest at the pact.

In Baghdad’s crowded Shia slum of Sadr City—the cleric’s main bastion of support—followers listened to fiery Friday sermons as Iraqi forces fanned out across the neighbourhood and US attack helicopters hovered overhead.

“We condemn the agreement and we reject it, just as we condemn all injustice,” Sheikh Hassan al-Husseini told worshippers. “No, no to America, No, no to colonialism, No, no to Satan!”

They poured into the streets, waving large black flags, flagellating themselves with chains and burning American flags to protest against the “US occupier.”

Sadr aide Aws al-Khafaji told reporters in the southern Shia holy city of Najaf that the movement would “keep up its rejection of this humiliating accord and resist through all means.”

Sadr had vigorously opposed the signing of any US agreement, but reaction among imams was mixed to the accord, which was approved by the country’s main Shia, Sunni, and Kurdish political blocs.

In the Sunni town of Samarra north of Baghdad, Sheikh Ahmed al-Samarraie said the agreement was “in the interests of Iraq, the Iraqi people, and Islam,” warning that the country needed US forces to protect it from Shia-led Iran.

“There is an enemy waiting to ambush Iraq when the American forces leave,” he said. “I call on the American forces not to withdraw from Iraq until Iraqi forces are able to protect security and are stronger than Iran.”

The agreement will see US troops withdraw from all cities and towns by the end of June and from the rest of the country by 2011, eight years after the US-led invasion that toppled Saddam Hussein and plunged the nation into chaos.

Iraq has seen dramatic improvements in security over the past year but certain regions still suffer from near-daily bombings and attacks.

Friday’s blast bore the hallmarks of Al-Qaeda in Iraq, which has carried out scores of massive bombings targeting Shia civilians since the 2003 invasion.

US and Iraqi forces allied with local Sunni militias have largely succeeded in flushing Al-Qaeda fighters out of their former strongholds, but the group retains the ability to regularly carry out smaller attacks.

The pact will be sent to Iraq’s presidential council next week, which will have 10 days from Sunday to ratify the deal. In the unlikely case it rejects the pact, the agreement will be sent back to parliament.