BAGHDAD, Iraq (CNN) -- Prime Minister Nuri al-Maliki is calling on political parties to unite against armed groups in Iraq, a spokesman said Sunday, warning that "Iraq cannot be the new Somalia."
Children inspect a car Sunday struck by a U.S. missile during an overnight airstrike in Baghdad's Sadr City.
"It is a clear message," al-Maliki spokesman Ali al-Dabbagh said of the situation in Iraq. "We cannot accept the presence of armed groups."
Somalia has been mired in chaos since 1991, when warlords overthrew dictator Mohamed Siad Barre and then turned on each other.
Shiite cleric Muqtada al-Sadr fired back at al-Maliki with a statement posted on loyalist Web sites Sunday, saying, "As far as I'm aware, the Iraqi forces supported by the occupation forces attacked some of our believer brothers."
"They killed them in the most gruesome of ways and then burned them, and refused to hand over their pure bodies for burial," he said, referring to clashes in Nasiriya on Saturday that left 16 militiamen dead and another 22 wounded. Eleven police officers were also wounded in the fighting.
Al-Sadr called for three days of mourning and demanded Iraqi lawmakers condemn the alleged attacks and "put an end to such a massacre under government cover."
The cleric also condemned a visit by U.S. Secretary of State Condoleezza Rice, who arrived in Baghdad on Sunday for unannounced talks with Iraqi leaders in Baghdad's International Zone, the heavily fortified district -- known also at the Green Zone -- that houses American and Iraqi governmental offices. Watch a report on Rice's visit, fighting and political progress in Iraq »
Shortly before U.S. officials announced her arrival, the U.S. military shut down the district, a rare move that the military said was done for "force protection purposes."
Earlier in the day, a lawmaker and member of al-Sadr's political bloc issued an ultimatum demanding al-Maliki's government immediately end its attacks on Shiite militias, or "all options are open to us."
Sadrist lawmaker Fawzi Tarzi also condemned the government's call to disband al-Sadr's Mehdi Army, saying that the demand "will mean the end of al-Maliki's government."
"And therefore the siege of Sadr City and Shula should end immediately or all options are open to us," Tarzi said. "There is a fierce military and media campaign and a dirty political conspiracy planned and supported by the occupier against the Sadr trend."
Baghdad's Sadr City has been the scene of many clashes in recent weeks between U.S. and Iraqi Security Forces and the Mehdi Army.
During Sunday remarks, Rice praised the Iraqi military for its recent operations targeting Shiite militants in Basra, an al-Sadr stronghold, saying it "fought very bravely in this recent operation."
She added that al-Maliki's government has shown it "will take on any group in their country, no matter what sect, that challenges the rule of law and the legitimate authority of the national government."
Tarzi's comments also follow airstrikes and firefights Saturday that left seven Shiite militants dead in Sadr City.
Sadr City has been the scene of many clashes in recent weeks between U.S. and Iraqi security forces and the Mehdi Army.
Tarzi called on humanitarian organizations and the world media to visit Sadr City to see what he described as a "humanitarian tragedy."
The Baghdad neighborhood is plagued with "random airstrikes and raids," which are causing a deteriorating humanitarian situation, he said.
More than 400 people have died and 1,300 have been wounded in the attacks, Tarzi said, citing hospital figures.
Al-Sadr on Saturday gave his "last warning" to the Iraqi government that he would "declare a war" unless U.S. and Iraqi forces stop their assaults on his followers.
Loudspeakers at Sadr City mosques announced al-Sadr's warning Saturday evening, calling for followers to fight the "occupier," a witness said.
According to the Interior Ministry, Saturday's Sadr City clashes killed nine Iraqis and wounded 15 others. It said the clashes continued into Sunday morning.
Al-Sadr's threat was issued the same day that a man claiming to be the leader of al Qaeda in Iraq urged his fighters to launch an offensive against U.S. forces in the next few weeks.
The speaker was identified as Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, on several Islamist Web sites that posted the recording.
Within the the next month, militants should "offer the head of an American as a gift to the deceitful [President] Bush," he said.
The speaker also called for attacks on members of Iraqi awakening councils, a movement of mostly Sunnis who have joined forces with the U.S. and Iraqi governments in battling Islamic jihadists loyal to al Qaeda in Iraq.
Rice is scheduled to be in Kuwait on Tuesday's for the Iraqi neighbors conference.
She said she hopes the conference will "reinforce the really significant progress that Iraq has made since our meeting last November in Istanbul."
The first neighbors' conference in Sharm el-Sheikh, Egypt, in May addressed Arab concerns about the al-Maliki government and its inability to foster political reconciliation among Sunni, Shiite and Kurdish factions.
The second conference in November in Istanbul, Turkey, was largely overshadowed by an increase in fighting between Turkish forces and Kurdish rebels based in northern Iraq.
Other developments Sunday
• The former Iraqi general awaiting execution for leading the 1988 campaign against the Kurds was hospitalized Sunday after a three-day hunger strike, his defense attorney told CNN. Ali Hassan al-Majeed, a cousin of executed dictator Saddam Hussein, was taken to a U.S. military facility in the International Zone, his attorney said.
• Diyala operations commander Gen. Abdul Karim said officials received at least 47 unidentified bodies -- 21 from the town of Khalis and 26 from Muqdadiya. All appeared to have been dead for several months, a morgue official said.
• Gunmen set up a fake checkpoint Sunday and ambushed a minivan carrying college students in the northern city of Baquba. The gunmen shot and killed one person and wounded two others, Baquba police said. They kidnapped three students and a driver, police said.
• A roadside bomb struck a minibus near the southern city of Diwaniya, killing at least two civilians and wounding five others, an Interior Ministry official said.
• A mortar slammed into a soccer field in northern Baghdad's Shiite district of Kadhimiya, killing at least one civilian and wounding seven others, an Interior Ministry official said. E-mail to a friend
CNN's Jomana Karadsheh and Christine Theodorou contributed to this report.