The blast in the town of Musayib also wounded 16 people, said police Captain Muthana al-Ma'amouri.

"A man stopped his car outside a busy shop and said it was broken down, then he left. Minutes later the car blew up, " said town resident Ahmed Abbas.

Police said earlier the blast occurred near a Shi'ite shrine.

Just two hours earlier, powerful Shi'ite leader Abdul Aziz al-Hakim had urged his followers to stand firm against what he called an al-Qaeda campaign to ignite sectarian civil war with bombings like one on Friday that killed at least 70 people.

That triple suicide bombing, at the Buratha mosque in Baghdad, the biggest single suicide attack on a Shi'ite target since November 2005, raised fresh fears of a full-blown communal conflict, with the United States, Britain and the United Nations quickly calling for Iraqi unity.

On Thursday, a car bomb near one of the world's most sacred Shi'ite shrines killed at least 15 people in the southern town of Najaf.

Hakim's speech, delivered on the anniversary of the execution of top Shi'ite cleric Muhammad Baqir alSadr and his sister by Saddam Hussein, called for unity between Iraq's main Shi'ite, Kurdish and Arab Sunni communities.

But he also reminded majority Shi'ites of their decades of suffering under Saddam's Sunni-dominated regime and urged them to resist attempts by the al-Qaeda leader in Iraq, Abu Musab al-Zarqawi, to plunge the country into open civil war.

"(Sunni) militants and insurgents want to return Iraq to Saddam's formula, " said Hakim, leader of the proIranian Supreme Council for the Islamic Revolution in Iraq, a party in the ruling Shi'ite Alliance. "This nation will not fall into the trap of sectarian war that is being pursued by Zarqawi's groups."

Sectarian tensions have been rising since the bombing of a Shi'ite shrine on 22 February touched off reprisals and pushed Iraq to the brink of civil war.

Hundreds of bodies of people shot or strangled have turned up on Baghdad streets, bound, blindfolded and showing signs of torture.

The latest bombs provided more proof of the failure of Iraqi leaders to tackle violence as they struggle to form a government.

Hakim's alliance is under intense pressure to replace Ibrahim al-Jaafari as its nominee for prime minister to break the deadlock over post-war Iraq's first full-term government.