Iraqi police said that eight civilians were killed and seven wounded in an air raid on a house in Basra by US aircraft on Saturday.
The US military said it was looking into the report. Both US and British military aircraft have provided air support to Iraqi forces in southern Iraq.
A curfew is in place in the capital amid the violence, with restrictions set to be reviewed by the military command on Sunday.
"I call upon the Arab leaders to give the resistance its legitimacy and to stand by the Iraqi people, not against them"
Muqtada al-Sadr, Iraqi Shia leader
James Bays, Al Jazeera's correspondent in Baghdad, said on Saturday that missiles were still being fired.
"I heard six mortars or rockets - it's difficult to distinguish between the sound of mortars and Katyusha rockets - land in the Green Zone," he said.
Fighting has also been reported in the central city of Karbala.
Raed Jawdat Shakir, a local police chief, said on Saturday that 12 "criminals" had been killed in the city.
In an exclusive interview with Al Jazeera, al-Sadr called on the Arab League, the Organisation of the Islamic Conference and the United Nations to recognise "the Iraqi resistance".
"I appeal to these parties to add legitimacy to the resistance and to stand by, not against, the Iraqi people because the Iraqi people need Arabs as much as they need any other person," he said.
"Iraq is still under occupation and the United States' popularity is reducing every day and every minute in Iraq.
"I call, through Al Jazeera, for the departure of the occupying troops from Iraq as soon as possible."
Sadr City raid
The continuing violence comes after the US military said 13 suspected fighters were killed on Friday and 26 on Thursday in Baghdad operations.
A US helicopter fired a missile during Friday's fighting in Sadr City, killing at least four people.
The US military said it called in the air raid after coming under small arms fire and that those killed were Shia fighters.
But Iraqi police and hospital officials said five civilians had been killed.
Friday's attacks on the Green Zone prompted the US state department to order embassy personnel to stay inside.
At least two of the rounds struck the offices of Tariq al-Hashemi, the Sunni vice-president, killing two guards and wounding four, according to Lubna al-Hashemi, his daughter and executive secretary.Air support
In Basra, US-led forces entered the fighting for the first time, carrying out bombing raids in the city overnight, a British military spokesman said.
Major Tom Holloway said that British forces based at Basra airport had been providing air support and surveillance over the city, as well as refuelling Iraqi helicopters and transport aircraft.
Parliament set up a committee led by the Sunni Arab speaker to try to mediate an end to the violence, Bassem Sharif, a member of the Fadhila party, said.
However, the country's largest Shia bloc, the United Iraqi Alliance (UIA), boycotted the emergency session, arguing that the crackdown in the south is a question of law and order, not legislative policy.
The Dawa party of al-Maliki, who is personally supervising the military operation in southern Iraq, is a member of the UIA.
Falah Shanshal, an MP from the Sadrist bloc, told Al Jazeera that al-Maliki's offer to reward fighters for turning over their weapons was "a cheap stunt".
"This is the approach of tyrants ... they are not achieving anything in Basra and they are relying on the occupations air power and those in Basra are collaborating with the occupations to kill their own people," he said.
Al-Maliki has pledged "no retreat" in the fight against Shia militia forces.
George Bush, the US president, said that the violence in Iraq was a "defining moment" for the country and a key test for al-Maliki's government.
"This is a test and a moment for the Iraqi government which strongly has supported prime minister Maliki's actions," he said.
"It is an interesting moment for the people of Iraq because in order for this democracy to survive they must have confidence in their government's ability to protect them and to be even-handed." Fierce clashes
Fierce clashes erupted in the southern city of Nasiriyah early on Friday between Iraqi forces and Shia fighters, killing at least four policemen, a local police official said.
|Police and hospital officials said five people |
died in a US raid on Sadr City [AFP]
In the southern city of Kut, 45 people were reported dead and 87 wounded from at least three days of fighing.
Helicopters dropped leaflets on Basra calling on residents to help the government in its fight "to rid Basra of outlaws".
Few journalists have been able to travel to the southern city, but witnesses said that Basra's streets were deserted - with shops and businesses shut.
Hassan, a resident of Basra, told Al Jazeera: "For two days now, we woke up to sounds of explosion - we have never witnessed such huge attacks in Basra."
He said all roads have been blocked and Mahdi Army fighters attacked Iraqi forces from residential and commercial blocks.