Nearly 50 people were killed and more than 130 wounded on Friday as the unrest fanned out across central and southern Iraq, pitting al-Sadr loyalists against British troops in Basra, Italian troops in Nasiriya and against US troops in Shia areas of Baghdad.
Some reports say US marines have killed an estimated 300 al-Sadr fighters in the last two days in Najaf alone, but a spokesman for the Shia leader denied this.
Sheik Raid al-Kathimi said only 36 members of the Mahdi Army have died in fighting across Iraq since Thursday.
Columns of thick black smoke could be seen rising up from Najaf, as residents stayed at home with their doors bolted and al-Sadr fighters took control of the streets.
Sixteen people were killed, including one US soldier, and more than 100 wounded in the city, reported our correspondent.
US planes fired rockets over Najaf, an al-Sadr stronghold which saw major fighting during the Mahdi Army's first standoff with the occupation troops.
One ambulance was set alight and burnt-out civilian vehicles littered the deserted streets, said an AFP correspondent.
Mahdi Army fighters have taken
on British, Italian and US troops
Only the sound of sporadic gunfire could be heard early on Friday.
Power lines were also cut.
At 4:00am (0000 GMT) four fighters attacked a police station in the eastern part of the city. No casualties were reported in the incident.
In Baghdad, at least 26 people were killed and 90 wounded in fighting pitting US troops and Iraqi security forces against Mahdi Army fighters in their stronghold of Sadr City, medics said Friday.
One mortar round landed near the Ashtar Sheraton and Palestine Meridien hotels, where a large number of journalists and foreign businessmen were residing, reported Aljazeera's correspondent.
The Sadr General Hospital said 18 bodies had been brought in and in addition to 73 injured people, including two women and four children.
Streets battles have broken out
afresh in the capital's Sadr City
In the Al-Shuader hospital, eight people were reported killed and 17 wounded. Two other hospitals reported 10 wounded between them.
Two civilians were killed and 13 wounded as US occupation forces, backed by airpower, fought resistance fighters in Samarra, north of Baghdad, medics said Friday.
The fighting was concentrated at the al-Bonisan and al-Jibairiya districts, reported our correspondent.
Three children were among the wounded, said a doctor at the
city's main hospital.
Fighting began late on Thursday near a bridge over the Tigris, said police colonel Abd al-Haq Ismail.
An AFP correspondent said US planes fired 11 rockets in the area.
In the southern city of Nasiriya, Italian forces clashed with Shia fighters in the early on Friday and tensions were still high, an Italian military spokesman said.
In more than a dozen attacks that began shortly after midnight (2000 GMT Thursday), Mahdi Army fighters fired rocket-propelled grenades, mortars and light arms at Italian patrols, key installations such as a power plant and an Iraqi police base, the Italian army said.
"It has been an extremely tense night and we are maintaining maximum alert," said Captain Ettore Sarli, chief spokesman for Italian occupation forces in Nasiriya.
"We are seeking mediation with the
militia via the
governor of the city"
Captain Ettore Sarli,
Chief Spokesman, Italian occupation forces in Iraq
"An Italian task force has control of the centre of Nasiriya and its bridges, and we are seeking mediation with the militia via the governor of the city," he said.
The Mahdi Army claimed to have destroyed at least four Italian armoured trucks in the fighting. Sarli confirmed various attacks on Italian patrols, but said there was no indication so far that four military vehicles had been destroyed.
Al-Sadr's militia also said it had attacked British forces in the southern city of Amara, but that claim too could not be independently confirmed.
The clashes come after a two-month uprising by al-Sadr's followers in April and May which led to bloodshed across southern Iraq. A tentative truce was struck in June, but now appears to have broken down.