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

The Sunni Iraqi Accordance Front said they will not participate in the conference until Shiite lawmakers address their political demands. They say Prime Minister 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?” a spokesman for the Sunni front, Saleem Abdullah, said. “There are many points that are still not fulfilled.”

America 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 Cheney and Senator McCain to tout security gains and stress Washington’s commitment to fighting insurgents in Iraq.

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

Mr. al-Maliki opened the reconciliation meeting a day after a female suicide bomber struck Shiite worshippers in the holy city of Karbala, killing at least 49 people, according to an official and a witness. The blast was the deadliest in a series of attacks that left at least 78 Iraqis dead yesterday.

In his opening statement, Mr. 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,” Mr. al-Maliki said.

In his address, Mr. 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, Mr. al-Maliki said, also could open the door to foreign influence and compromise Iraq’s constitutional principles.

The female bomber in Karbala struck after worshipers 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.

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.

In other violence today, 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.