The blast, which occurred in the early morning, also badly damaged a neighbouring home in Iskandiriyah, which lies within a confessionally mixed area known as the Triangle of Death because of frequent attacks since the 2003 US-led invasion.

Mohammed al-Shammari, a doctor at the main hospital in the nearby city of Hilla, said six people were killed and 11 others were wounded in the explosion.

Among the injured were women and children, he said. The wounded included four who were badly hurt.

A police lieutenant in Iskandiriyah also put the toll at six dead, including two children, and six wounded.

The family whose house was bombed were members of the Shiite Al-Massudi tribe, he said.

Two separate attacks south of the disputed northern oil city of Kirkuk, meanwhile, left one anti-Qaeda militiaman dead and two people wounded, local police said.

And in the restive central province of Diyala, an Iraqi soldier was gunned down in front of his home in the town of Khales, and two people were wounded by a roadside bomb in the provincial capital Baquba, an army officer said.

Violence in Iraq has declined from its peak in 2006 and 2007 but attacks remain common. A total of 259 Iraqis were killed in attacks in July, the second-highest monthly figure for 2011.

The letter, released on Saturday in the Shiite cleric's base in the shrine city of Najaf, came after Baghdad agreed to open talks with Washington for a training mission post-2011, when all US troops are due to have left.

"We will treat anyone who stays in Iraq as an oppressive occupier that should be resisted through military means," Sadr, who divides his time between Iran and Najaf, said in a letter released by his office.

"The government that agrees to their stay, even if it is for training, is a weak government."

In another letter released by his office on Sunday, he said that "we should stand together to reject the presence of the infidel occupier and the armies of darkness, and we refuse any presence of bases or trainers."

His movement issued a code of conduct to followers last month stating they must consider "as enemies only the United States, Britain and Israel, and take into account that military resistance should be conducted by specialists."

Sadr's remarks come after Iraqi political leaders agreed on Wednesday to start negotiations with Washington on a US military mission to train Iraqi security forces.

Unresolved issues remain over the size of the force, the duration of its stay, and whether its members would enjoy immunity from prosecution.

About 47,000 US troops are still stationed in Iraq, all of whom must leave by the end of the year under the terms of a 2008 bilateral security pact, which would remain in force if a training deal is not agreed.

US and Iraqi military officials assess Iraq's security forces capable of maintaining internal security, but say the country is lacking in terms of capacity to defend its borders, airspace and territorial waters.

Sadr's movement has 40 deputies in parliament and seven ministers in Prime Minister Nuri al-Maliki's national unity government.

And before it was disbanded in 2008, Sadr's Mahdi Army numbered some 60,000 fighters with fierce loyalty to the cleric. It fought bloody battles with the US army in the years following the 2003 invasion which ousted Saddam Hussein.

On July 10, Sadr said he would not revive the Mahdi Army, complaining it had been infested with "criminals."