Wednesday's attack on the Askariya shrine in Samarra, which was blamed on Sunni extremists with links to al-Qaeda, stoked fears of a surge in violence between Muslim sects. A bombing at the same mosque complex in February 2006 that destroyed the shrine's famed golden dome unleashed a bloodbath of reprisals.

Increased US and Iraqi military patrols crisscrossed the streets of the Iraqi capital, and additional checkpoints were set up along roads leading to Sadr City, witnesses said.

Hundreds of residents marched peacefully through the streets of that teeming neighbourhood, a stronghold of Shia cleric Muqtada al-Sadr's Mahdi Army militia. Demonstrations also took place in Kut, Diwaniyah, Najaf and Basra all predominantly Shia cities in the south.

A ban on vehicular traffic was expected to remain in place in Baghdad until Saturday.

Attacks on Sunni mosques began within hours of Wednesday's bombings in Samarra.

Police in the southern city of Basra said Thursday that four people were killed and six wounded in attacks on the Kawaz, Othman, al-Abayshi and Basra Grand mosques on Wednesday, all involving rocket-propelled grenades that also damaged the buildings. Basra is Iraq's second-largest city, 340 miles southeast of Baghdad.

Four Sunni mosques near Baghdad also were attacked or burned within several hours of the Samarra bombings, police said.

One of those mosques, which had been only partly destroyed, was a target again Thursday, police said. Around 4 am, attackers broke into the Hateen mosque in Iskandariyah, 50km south of Baghdad, and planted bombs inside.

Flames from a huge explosion destroyed most of the building, and a woman and child in a nearby apartment were wounded, an Iskandariyah police officer said on condition of anonymity because he was not authorised to release the information.

Gunmen also tried to storm the nearby al-Mustafa mosque early Thursday, and exchanged fire with guards before Iraqi soldiers arrived and stopped them, police said. There were no immediate reports of casualties.

In Mahaweel, 58km south of Baghdad, gunmen opened fire on the al-Basheer mosque at dawn Thursday, police said. They forced guards to leave, then set fire to the mosque, a local police officer said on the same condition of anonymity. The building was partly damaged, he said.