A prominent Sunni Arab group charged Friday that some officials in the Iraqi government have links with Shiite militias involved in sectarian violence and said authorities should be held responsible for any attacks by the armed groups.

The Iraqi government said the group’s claims were false and could incite rebellion.

Police in the southern city of Basra reported that an American civilian and two Iraqis were abducted Friday, according to Voices of Iraq, an independent news agency. The U.S. Embassy said it was investigating the report.

A Sunni clerical group, the Association of Muslim Scholars, said it had obtained information that militias were planning to attack neighborhoods in Baghdad, in line with bloody assaults this year pitting members of Iraq’s majority Shiites against Sunni Arabs who dominated the country under Saddam Hussein.

“We also have come to know that some officials in this government know of this criminal scheme, which raises suspicions that they are collaborating with these militias,” the association said.

“The Association of Muslim Scholars holds the current Iraqi government and the occupation forces responsible for any injustice against Iraqi people,” said the group, which is believed to have links to the Sunni Arab-led insurgency fighting government and U.S.-led forces.

A significant portion of the Iraqi national police is believed to be aligned with militias, and U.S. officials have said efforts are under way to weed out corrupt security agents.

The office of Prime Minister Nouri al-Maliki said the Sunni group’s statement was wrong.

“What has been written in the statement of the Association of Muslim Scholars is absolutely incorrect and it could provoke sedition,” al-Maliki’s office said. “We hold the association responsible for anything that could happen as a result of this.”

In Washington, President Bush said Thursday that he wished Saddam’s execution “had gone in a more dignified way,” referring to the unruly scene in the execution chamber — recorded on a cell phone camera — during the hanging of the deposed president Dec. 30.

Bush said he spoke with al-Maliki about Saddam’s last moments on a secure video hookup. The two leaders also discussed Iraq’s violence, and Bush said he would announce next week his decisions about how to proceed with the war.

A defense official, who insisted on anonymity because formal announcements are still pending, said that Bush wants to replace Abizaid with Adm. William Fallon, the top U.S. commander in the Pacific and that Casey’s replacement would be Army Lt. Gen. David Petraeus, who headed the effort to train Iraqi security forces.

Giving Fallon and Petraeus the top military posts in the Middle East would help Bush assert that he is taking a fresh approach in the region. Both Abizaid and Casey have expressed reservations about the potential effectiveness of boosting troop strength in Iraq.

A senior administration official said Bush would nominate Zalmay Khalilzad, the outspoken U.S. ambassador to Iraq, as the U.S. envoy to the United Nations. He would replace John Bolton, whose appointment to the U.N. job expired recently.

Khalilzad, who was born in Afghanistan, is likely to be replaced in Baghdad by Ryan Crocker, a veteran American diplomat, said the official, who agreed to discuss the matter only if not quoted by name because he was not authorized to make an announcement for the White House.

On Friday, mortar rounds killed four civilians on Baghdad’s outskirts, and gunmen attacked an Iraqi army checkpoint north of the capital, killing four soldiers.

The mortar attack occurred in the Shiite neighborhood of Zaafaraniyah, nine miles southeast of the center of Baghdad, a police officer said on condition of anonymity because he was not authorized to talk to media. The attack killed four civilians and injured 11, he said.

The Iraqi soldiers were killed at dawn at a checkpoint in Duluiyah, 45 miles north of Baghdad, according to the joint operations office of Salahuddin province. Three other soldiers were wounded.

Also Friday, clashes broke out between Sunni Arab and Shiite militants in Baghdad’s mixed western Amil district, minutes after a mortar round hit a house in a Sunni neighborhood, injuring five civilians, police said. One Shiite militiaman was killed and three others were wounded.

The fighting ended when U.S. and Iraqi forces arrived, police said.

Police agents from the Interior Ministry detained three Iraqi insurgents linked to al-Qaida during a raid in Iskandariyah, 30 miles south of Baghdad, police Capt. Muthana Khalid said.

Separately, Iraqi troops captured four murder suspects in an operation Wednesday in Sadr City, a poor Shiite area in eastern Baghdad where militias have a strong presence, the U.S. military said.

The suspects were believed to be “leaders of a kidnapping and murder cell responsible for the deaths of Iraqi civilians,” and were suspected of directing mortar attacks linked to Baghdad’s sectarian war, the military said.

Also Friday, a bomb stashed in a garbage can at a market exploded, shaking parts of central Baghdad, but police said there were no reports of injuries.