A boycott by several political groups Sunday caused parliament to again put off a rancorous debate on a federalism bill that Sunni Arabs fear will split Iraq apart and fuel sectarian bloodshed.

Authorities reported finding 11 more bodies that appeared to be victims of the religious reprisal killings that have surged in recent months, while 18 Iraqis died in bombings and shootings across the country.

Prime Minister Nouri al-Maliki, meanwhile, postponed his first official visit to Iran, officials said. He was supposed to be in Tehran on Monday to affirm friendly relations but also discuss mutual respect for each nation's internal affairs. U.S. officials have accused Iran of not doing enough to stop militants infiltrating into Iraq.

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The federalism bill, submitted by the largest Shiite Muslim bloc, the United Iraqi Alliance, calls for a three-part federation that would create a separate autonomous state in the predominantly Shiite south much like the zone run by Kurds in the north.

Many Sunni Arabs, whose minority dominated during Saddam Hussein's regime, are horrified by the idea. Both the north and south are rich in oil, and Sunnis fear they will end up squeezed into Baghdad and Iraq's western provinces, which have no natural resources.

Vehement objections from Sunni Arabs and an apparent split among Shiites led leaders to delay debate until Sept. 19. A previous attempt to discuss the bill Thursday set off acrimonious squabbling that led parliament speaker Mahmoud al-Mashhadani to recess that session.

The Iraqi Accordance Front, the largest Sunni bloc, and another Sunni party, the National Dialogue Front of Saleh al-Mutlaq, boycotted Sunday's parliament sitting to protest the bill.

They were joined by the secular Iraqi National List led by former prime minister Ayad Allawi and by lawmakers loyal to radical Shiite cleric Muqtada al-Sadr, whose bloc usually supports the main Shiite coalition, the United Iraqi Alliance.

"Federalism is a preliminary step to dividing and separating Iraq. I call on Iraqis to confront this draft," said Adnan al-Dulaimi, head of the Iraqi Accordance Front.

Ayad Jamal al-Deen, a member of the National List, warned that federalism is sowing division among lawmakers.

"It is unwise to create a problem that provokes argument between the blocs," he said, adding that this could undermine the Shiite prime minister's national reconciliation plan that is trying to bridge religious, political and ethnic divides.

Parliament's Shiite deputy speaker, Khalid al-Atiya, defended the bill, denying that federalism is meant to destroy Iraq as a unified state.

The idea that the legislation will divide the country "is a misleading one and agitates public opinion without any reason," al-Atiya told reporters. "Issuing legislation for federalism doesn't mean that we will start the measures of establishing autonomous regions the next day."

The concept of federalism is enshrined in the new Iraqi constitution, and there is already an autonomous Kurdish region in the north. However, special legislation and a referendum would be needed to turn Iraq into a full federation.

Animosity between Sunni and Shiite Arabs has fueled an escalation in sectarian killings since a bomb wrecked a Shiite shrine in Samarra last February.

Authorities found 11 bodies Sunday that bore the hallmarks of sectarian reprisals.

Six were floating in the Tigris River near Kut, a city 100 miles southeast of Baghdad. They had been blindfolded, had their hands and feet tied and all showed signs of torture, officials at the Kut morgue said.

Two bodies — one decapitated — were found in a drainage ditch in Musayyib, about 40 miles south of Baghdad. Three more were found in the Tigris near the Duluiyah bridge, 47 miles north of the capital.

There were indications a joint U.S.-Iraqi security operation in Baghdad could be expanding into the sprawling Shiite slum of Sadr City, which is home to more than 2.5 million people and a stronghold of al-Sadr, who heads the Mahdi Army militia.

Residents in western and central parts of Sadr City said security forces used loudspeakers urging people to allow searches of their homes.

The Defense Ministry said last week that Sadr City would be searched as part of Operation Together Forward, a crackdown targeting the capital's most violent districts in phases that has seen an extra 12,000 Iraqi and U.S. soldiers deployed in the capital.

A roadside bomb near Baghdad's central Tahrir Square, a popular commercial area, killed at least five people and wounded 17, police said.

Less than an hour later, a bomb went off behind a police station in the city's al-Alwiya district, killing a police officer and wounding five police commandos and two civilians.

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