A UN envoy urged Iraq's government on Saturday to halt a slide into civil war and stop the "cancer" of sectarianism from destroying the country.
As a curfew on Baghdad was extended until Monday, derailing a trip to Iran by Iraqi President Jalal Talabani, the United Nations' representative said car bombs on Thursday that killed more than 200 Shi'ites and "blind acts of revenge" were "tearing apart the very political and social fabric of Iraq".
"No country could tolerate such a cancer in its body politic," Ashraf Qazi said in a statement.
Talabani was to have flown to Tehran on Sunday, but his spokesman Hiwa Othman said it was now hoped the trip could go ahead on Monday after a third day of curfew in Baghdad. Talabani had said he would not go to Tehran until Baghdad airport reopens.
The president met government leaders again on Saturday evening to discuss how to resolve the current crisis and avert a worsening of violence. An official familiar with the talks said a joint statement on security measures would be made on Sunday.
Talabani's visit to anti-American Iranian President Mahmoud Ahmadinejad, whom Washington accuses of backing militant fellow Shi'ites in Iraq, is part of efforts to involve its neighbours in efforts to prevent civil war. Othman said that contrary to some speculation, Syria's president would not join the meeting.
US President George W Bush appears sceptical of what his adversaries Iran and Syria are willing to do. However, Vice President Dick Cheney was in Saudi Arabia on Saturday, expected to discuss Saudi influence over Iraq's restive Sunni minority.
Bush is expected to meet Maliki in Jordan on Wednesday, despite a threat by a key Maliki ally, radical Shi'ite cleric Moqtada al-Sadr, to boycott the government if it goes ahead.
The Shi'ite-led government has called for calm, desperate to avert the sort of sharp escalation in violence that followed an attack on a Shi'ite shrine in Samarra in February.
Fearful Iraqis spent sleepless nights guarding their homes after gunmen attacked mosques and burned homes in a Sunni enclave on Friday following the worst bomb attack since Saddam Hussein's overthrow in April 2003.
Abu Marwah, who lives in the Jamia area of mainly Sunni west Baghdad, said: "All the men in the area were on alert ... we received information that militias were expected to attack. Of course we all had our Kalashnikovs."
The city of 7 million was under a tight curfew imposed after 202 were killed in Sadr City, stronghold of Moqtada al-Sadr's Mehdi Army militia, which Sunni Arabs blame for thousands of death squad killings since the Samarra bombing.
"Everybody is tense, everybody is expecting something may happen at any moment," said Abu Marwah, 40, who spent much of the night on the roof of his home, keeping watch, gun to hand.
Mortar rounds hit Sadr City and other districts after dark on Saturday, causing a number of casualties, police said.
An Interior Ministry source said the bodies of 30 victims of violence were picked up in Baghdad on Friday and 17 on Saturday. Yarmouk hospital in west Baghdad said it took in 33 in the two days. Hakim al-Zamily, a deputy health minister from Sadr's faction, said 33 Shi'ites were killed in west Baghdad in sectarian attacks. Police and the hospital could not confirm it.
In apparent revenge for the Sadr City bombings, mosques and homes were attacked in a Sunni enclave in northwest Baghdad on Friday, although the government and US military questioned on Saturday accounts from residents and police of up to 30 dead.
Police found the bodies of 21 men and boys from an extended Shi'ite family on Saturday in a mainly Sunni Arab village in Diyala province northeast of Baghdad, security sources said.
Despite centuries of harmony between Shi'ite Muslims and the Sunni minority, three years of bigotry and bloodshed have turned Baghdad's rich mix of communities into a patchwork of fearful, heavily armed and mutually hostile sectarian redoubts.
Among Iraq's leaders, too, tensions have risen sharply as Maliki's 6-month-old unity government struggles to function. Iraq's top Sunni cleric, now in exile and wanted on terrorism charges, said: "This government ... exploits sectarianism."
(Additional reporting by Claudia Parsons, Ahmed Rasheed, Ross Colvin and Alastair Macdonald in Baghdad, Jonathan Wright in Cairo and Caren Bohan in Washington)