US forces have been drawn deeper into Iraq's four day-old crackdown on Shi'ite militants, launching air strikes in Basra for the first time and battling militants in Baghdad.
The fighting has exposed a deep rift within Iraq's majority Shi'ite community and put pressure on Prime Minister Nuri al-Maliki, whose forces have failed to dislodge fighters loyal to cleric Moqtada al-Sadr from Iraq's second largest city.
Iraqi authorities shut down Baghdad with a strict curfew on Friday which seemed to reduce the rocket and mortar barrages that have wreaked havoc in the capital this week. Lawmakers, including those loyal to Sadr, met to seek an end to the impasse.
The government says it is fighting "outlaws", but Sadr's followers say political parties in Maliki's Shi'ite-led government are using military force to marginalize their rivals ahead of local elections due by October.
The Iraqi ground commander in Basra, Major-General Ali Zaidan, said his forces had killed 120 "enemy" fighters and wounded around 450 since the campaign began.
But Reuters television footage from Basra showed masked gunmen from Sadr's Mehdi Army still in control of the streets, openly carrying rocket launchers and machine guns.
A British Ministry of Defence spokesman said US warplanes had opened fire in Basra for the first time in support of Iraqi units on the ground. British troops, which patrolled Basra until December, have so far remained on a base outside the city.
GUNMEN SEIZE NASIRIYA
A Reuters witness said Mehdi Army gunmen had seized control of Nassiriya, capital of the southerly Dhi Qar province. Mehdi Army fighters have held territory or fought with authorities in Kut, Hilla, Amara, Kerbala, Diwaniya and other towns throughout the Shi'ite south over the past several days.
In Baghdad there have been clashes in at least 13 mainly Shi'ite neighborhoods, especially Sadr City, the vast slum named for the cleric's slain father where his followers maintain their power base.
"There have been engagements going on in and around Sadr City. We've engaged the enemy with artillery, we've engaged the enemy with aircraft, we've engaged the enemy with direct fire," said Major Mark Cheadle, spokesman for US forces in Baghdad.
In one strike before dawn, a US helicopter fired a hellfire missile at gunmen firing from the roof of a building, killing four of them, Cheadle said. A Reuters photographer there filmed windows blown out of cars and walls pocked with shrapnel.
US forces said they killed 27 fighters in operations in the capital on Thursday.
In Nassiriya, a Reuters reporter said he could see groups of fighters with machineguns and rocket-propelled grenade launchers. The sound of sporadic gunfire echoed through the streets. Police appeared to be staying in their stations.
Militants have also taken control of the town of Shatra, 40km to the north, he said, citing witnesses.
Maliki on Wednesday gave militants in Basra 72 hours to surrender. With that deadline looming on Friday, he announced they would be given until April 8 to hand over some weapons.
"All those who have heavy and intermediate weapons are to deliver them to security sites and they will be rewarded financially," he said in a statement issued by his office.
Oil exports from Basra of more than 1.5 million barrels a day provide 80 per cent of Iraq's government revenue. An explosion at a pipeline damaged exports on Thursday, but they were back to normal on Friday.
Parliament speaker Mahmoud Mashhadani said representatives of Shi'ite and Sunni parties, including those loyal to Sadr, had agreed to attend a special session at 3pm (1200 GMT).
Sadr, who helped install Maliki in power after an election in 2005 but later broke with him, has called for talks with the government. But Maliki has vowed to battle what he calls criminal gangs in Basra "to the end".
The clashes have all but wrecked a truce that Sadr imposed on his Mehdi army last August, which Washington had said helped curb violence.
US President George W Bush has praised Maliki's "boldness" in launching the operation, the largest military campaign carried out yet by Maliki's forces without US or British combat units. Bush said it showed the Iraqi leader's commitment to "enforce the law in an even-handed manner".
Sadr's followers have staged a "civil disobedience" campaign, forcing schools and shops to shut, and Sadr has threatened a "civil revolt" if the crackdown is not halted.