Iraq's main Sunni bloc boycotted a conference Tuesday aimed at reconciling the nation's sectarian groups, a sign of the deep schisms still facing this country.

Members of the Sunni Iraqi Accordance Front said they would not participate in the conference until Shiite lawmakers address their political demands. They say Prime Minister Nouri al-Maliki, a Shiite, has failed to release detainees not charged with specific crimes, has not disbanded Shiite militias and has not sufficiently included Sunni lawmakers in decision-making on security issues.

"How we can attend a reconciliation meeting?" said Saleem Abdullah, a spokesman for the Sunni front. "There are many points that are still not fulfilled."

The U.S. is pressing the Iraqis to achieve national reconciliation, warning that progress toward that goal is necessary to guarantee long-term American support.

The conference comes after visits by Vice President Dick Cheney and Sen. John McCain to tout security gains and stress Washington's commitment to fighting insurgents in Iraq.

Cheney spent Monday night at the U.S. military base in Balad, 50 miles north of Baghdad, before flying to Irbil in the Kurdish region of northern Iraq Tuesday. There, he was to meet with Massoud Barzani, head of the regional administration in the semiautonomous area. McCain traveled to Jordan on Tuesday.

Al-Maliki opened the reconciliation meeting a day after a suicide bomber struck Shiite worshippers in the holy city of Karbala, killing at least 50 people, according to an official and witness. The blast was the deadliest in a series of attacks that left at least 79 Iraqis dead on Monday.

In his opening statement, al-Maliki said reconciliation was not intended to harm the interests of any group but was "a boat that saves us and takes us to safety."

"From the first day, we said national reconciliation is not a political slogan, but a complete strategical vision to reconstruct Iraq," al-Maliki said.

In his address, al-Maliki noted many in the government continued to doubt the success of reconciliation. But he urged lawmakers to view differences in opinion as political progress, not disagreement that threatened to unravel national unity.

A heated debate over differences, al-Maliki said, also could open the door to foreign influence and compromise Iraq's constitutional principles.

He acknowledged in a later briefing for reporters that much work remains to bridge Iraq's sectarian divides.

In one case, Iraqi leaders also have made little progress in resolving disagreements over the execution of three Saddam Hussein-era Sunni officials for their role in the brutal gassing of Kurd civilians in northern Iraq in 1988.

But in a statement Tuesday, Iraq's cabinet backed plans to carry out the death sentences of Hassan al-Majid, Saddam's henchman and cousin known as "Chemical Ali," within the month.

Iraqi Sunnis have expressed anger over plans to execute former defense minister Sultan Hashim al-Taie, despite his conviction in Iraqi courts. Hussein Rashid Mohammed, the former deputy director of operations for the Iraqi armed forces, was also sentenced to death.

The bomber in Karbala struck after worshippers gathered at a sacred historical site about half a mile from the golden domed shrine of Imam Hussein, a grandson of the Prophet Muhammad who was killed in a seventh-century battle.

A police officer, speaking on condition of anonymity because he wasn't authorized to release the information, said the attacker was a woman — as did a witness. The Interior Ministry, in a statement on Tuesday, identified the attacker as a man.

Female suicide bombers have been involved in at least 20 attacks or attempted attacks since the war began in 2003, including the bombings of two pet markets in Baghdad that killed nearly 100 people last month.

The national conference coincides with the release of a United Nations report that says record numbers of Iraqis sought asylum in the European Union last year, despite a sharp reduction in violence that followed the surge of U.S. forces.

Asylum requests from Iraqis shot up to 38,286 in 2007, from 19,375 in 2006, according to the report, making Iraqis the single largest group seeking refuge in the EU.

Al-Maliki said Tuesday that Iraqi officials were working to return Iraqi refugees home.

In other violence Tuesday, a roadside bomb near a gas station in northern Baghdad killed three people, including two police officers, police officials said on condition of anonymity because they were not authorized to discuss the attack.