A car bomb in a Shi'ite holy city and bloody battles around Sunni mosques in Baghdad have heightened fears that Iraq is heading for civil war.
Iraqi Defence Minister Saadoun al-Dulaimi called for calm and told a live televised news conference on state television: "If there is a civil war in this country it will never end."
Iraqi leaders are scrambling to break the round of tit-for-tat reprisals, sparked by a suspected al Qaeda bombing of a major Shi'ite shrine in Samarra on Wednesday.
A curfew declared yesterday in the capital has been extended until Monday morning.
The gravest crisis since the US invasion in 2003 threatens US plans to withdraw its 136,000 troops.
The biggest political bloc from the once-dominant Sunni Muslim minority said it might end a boycott of US-backed negotiations on forming a national unity government that Washington hopes can stifle sectarian strife that has killed more than 200 people in Baghdad in three days.
But Iraq's most prominent Sunni cleric, blaming Shi'ite police for attacking his home, said live on pan-Arab television during the gunbattle: "This is civil war declared by one side."
It seemed that shooting may have been linked, however, to a gun attack on the passing funeral cortege of a journalist killed as she reported from Samarra on Wednesday.
The same mourners were hit by a roadside bomb on their return from the burial in western Baghdad. The two attacks left three security men dead.
Thousands of untried, US-trained police and Iraqi troops kept traffic off the roads around Baghdad. The US military said it had a rapid reaction force standing by in the city.
South of the capital, a remote-controlled car bomb killed eight people and wounded 31 in the Shi'ite holy city of Kerbala. Overnight gunbattles around Sunni mosques in two parts of Baghdad were followed by the discovery of the bodies of 14 police commandos near one of the sites.
Police said it was not immediately clear how or when their colleagues were killed.
Gunmen wearing the black clothing preferred by some Shi'ite militias attacked two mosques in the south of the city with rifles and rocket-propelled grenades, police said.
Residents said local Sunnis defending one of the mosques appeared to fire both on the militiamen and on police commandos who intervened. Near Baquba, northeast of the capital, where religious tensions run high, police said gunmen killed 12 members of one family in their home in what they said was a sectarian attack on Shi'ites.
Rockets and mortars fell on the sprawling Shi'ite slum of Sadr City in eastern Baghdad. One destroyed a house and killed two women and a man and wounded a child, said a spokesman for the Shi'ite movement led by Moqtada al-Sadr.
Near the northern city of Kirkuk, a Katyusha rocket damaged a Shi'ite shrine overnight, police sources said.
Near Baquba, military sources said Iraqi troops killed four suspected Sunni insurgents and arrested 17.
The main Sunni political bloc, which raised hopes for stability by standing in a parliamentary election in December, pulled out of negotiations on a unity coalition with Shi'ites and Kurds after accusing Shi'ite leaders of fomenting violence.