"We will continue to stand up to these gangs in every inch of Iraq," he said in remarks broadcast on state-owned television on Saturday.
"There are some among us who are worse than al-Qaeda. Al-Qaeda is killing innocents, al-Qaeda is destroying establishments and they [Shia fighters] also," he said.
Late on Saturday, the Baghdad military command extended the curfew in the capital indefinitely.
The curfew, which was imposed late on Thursday, was originally set to expire on Sunday at 5am (0200 GMT).
James Bays, Al Jazeera's correspondent in Baghdad, said: "The curfew shows that the government is extremely nervous.
"Sunday should be a normal working day here in Iraq and I think they wanted to lift the curfew so that people could go about their normal business," he said.
|Shia fighters have continued to clash with|
Iraqi forces despite calls to surrender [AFP]
Police in Basra said on Sunday that 163 people have been killed and about 500 injured in sporadic clashes in the city between government forces and militias since Tuesday.
In the southern city of Nasiriyah, 67 people have been killed and another 137 wounded, local officials said.
At least 10 mortars fell into Baghdad's fortified Green Zone as sporadic fighting continued overnight into Sunday.
Bays told Al Jazeera that there is no evidence that a major Iraqi military operation is under way in Basra.
"[Iraqi forces] are having to rely, to an extent, on air power provided by... British and American aircraft and Predator unmanned aircraft with Hellfire missiles," he said.
"Al-Maliki says he will stay and that his men will fight to the end, but this operation looks like it is getting bogged down."
Tom Holloway, British military spokesman for Iraq, told Al Jazeera that British forces in Basra had fired artillery rounds at people they had identified as opposition fighters.
"We've been firing in support of Iraqi ground forces. They've been in contact, they've requested support from the coalition and artillery on a couple of occasions has been deemed the most appropriate response."
"We use our surveillance assets and conduct a collateral damage assessment. Obviously, once we've positively identified the target we make an assessment that we are able to attack it," he said.
Holloway said that British involvement in the operation is "entirely in line with the agreements with the government of Iraq", known as operational overwatch.
Iraqi police said that eight civilians were killed and seven wounded in an air raid by US aircraft on a house in Basra on Saturday.
US forces said they had killed 48 fighters in air strikes and gun battles across Baghdad on Friday.
Scores of people are also reported to have been killed in fighting in other towns across the south of the country.
Fighting has also been reported in the central city of Karbala.
Mahdi Army targeted
The Basra crackdown is aimed at disarming the city's warring Shia militias, including the Mahdi Army of al-Sadr, as well as crushing a number of criminal gangs.
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.
"The occupation is trying to divide Sunnis and Shias. It is trying to drive a wedge between Sadris and the Sunnis. I love the Sunnis. I am a Shia, but we are all Iraqis.
|An al-Sadr official said Iraqi troops in Baghdad|
tried to handover arms to the group [AFP]
"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."
Meanwhile, fighters loyal to al-Sadr rejected the prime minister's call to disarm.
"Al-Sadr has told us not to surrender our arms except to a state that can throw out the occupation," Haider al-Jabari, a member of the Sadr movement's political bureau, said.
On Thursday, al-Maliki said that Basra residents would receive a "reward" if they handed in "heavy and medium-size weapons".
However, in Baghdad an official from al-Sadr's bloc said Iraqi soldiers had attempted to hand their weapons over to him.
"We told them they should keep their arms. We gave them a Quran and they went back," Salman al-Afraiji said.
A curfew is in place in the capital,with restrictions set to be reviewed by the military command on Sunday.