Five American soldiers were killed south of Baghdad, including four in a single roadside bombing, the military said Sunday.
The leader of the largest Sunni bloc in parliament, meanwhile, issued an impassioned appeal for help from Arab countries against what he called Iranian-supported death squads and militias in the latest blow to the U.S.-backed Iraqi government's reconciliation efforts.
Adnan al-Dulaimi, the leader of the Iraqi Accordance Front, warned that Baghdad was in danger of falling into the hands of the "Persians" and "Safawis," using terms referring to Iran.
"Arabs, your brothers in the land of the two rivers and in Baghdad in particular are exposed to an unprecedented genocide campaign by the militias and death squads that are directed, armed and supported by Iran," al-Dulaimi said in a statement e-mailed to The Associated Press by his office.
Most of Iraq's neighboring countries are majority Sunni, while Iran and Iraq have mostly Shiite populations, raising regional concern about Tehran's influence over the Iraq Shiite-dominated government and security forces.
Al-Dulaimi's words reflected growing frustration among Sunnis with Iraqi Prime Minister Nouri al-Maliki's government, which is widely accused of having a Shiite bias and has failed to stop the execution-style killings believed carried out mainly by Shiite-led death squads. Bombings usually blamed on Sunni extremists also have persisted.
The U.S. military also has stepped up claims that Tehran is fueling violence in Iraq by supplying Shiite militias with training and powerful weapons. The Iranians have denied the claims.
Al-Maliki last week made his second trip to Iran since taking office in what many critics claimed was proof of Tehran's influence over his government. The Shiite leader defended the trip and said he would continue traveling to other countries to seek help in stemming the violence.
"Iraq has turned into the center of terrorism. Iraq will only succeed through reconciliation," he said at a separate news conference.
Al-Maliki also said he planned a meeting of political leaders to discuss reform demands made by various factions, including the Accordance Front, which has withdrawn its ministers from Cabinet meetings.
But al-Dulaimi's remarks made no mention of reconciliation efforts.
He said urgent action was needed against what he described as an organized campaign by Shiite militias to drive Sunnis from the capital.
"Areas such as Azamiyah, Sulaikh, Fadhil, Dora, Adil, Jami'a, Ghazaliyah, Amiriyah and Yarmouk are attacked daily by Iranian-made mortars that were given to militias to eradicate the Sunnis," the statement said, referring to neighborhoods in Baghdad.
He also made the point during a press conference at his house in Adil, a Sunni-dominated neighborhood in western Baghdad.
"I call on all Arabs, Muslims, presidents and kings and people to intervene and urge the Iraqi government to get out from this crisis and I call on them to stand beside Iraqis against violence and the oppression that come to us from Iran and its agents," he said.
The blast that killed the four soldiers and wounded four others occurred Saturday during combat operations south of the capital, the military said. Another soldier was killed Saturday by small-arms fire during a foot patrol southeast of Baghdad.
All the soldiers were assigned to Task Force Marne, which operates in an area with a volatile mix of Sunni and Shiite extremists.
U.S. and Iraqi forces elsewhere reportedly staged raids in a Shiite stronghold in Baghdad and the holy city of Kufa.
A police officer said two civilians were killed and four wounded when the joint forces backed by helicopters stormed into houses in Baghdad's Shiite district of Sadr City.
The officer, who spoke on condition of anonymity because he wasn't authorized to release the information, also said 16 people were detained. The U.S. military said it was looking into the report.
AP Television News footage and photos showed a crumpled white car and a truck pockmarked by shrapnel, with a pool of blood on the street. Dozens of men carried a black coffin in a funeral service for one of the purported victims.
Joint U.S.-Iraqi forces backed by air power also raided the house of an aide to radical Shiite cleric Muqtada al-Sadr in the holy city of Kufa, 160 kilometers (100 miles) south of Baghdad, according to al-Sadr's office.
The U.S. military had no immediate word on that report either. Sheik Fouad al-Turfi was detained, according to an official and a relative who declined to be identified because he feared retribution.
U.S.-led forces have routinely carried out raids searching for Shiite militants since they launched a Baghdad security crackdown nearly six months ago. On Wednesday, U.S. aircraft and soldiers attacked Shiite militia bomb makers accused of links to Iran, killing 32 suspected militants and detaining 12 others.
The raids have sent a strong message that U.S. forces plan no letup on suspected Shiite militia cells despite risks of upsetting al-Maliki and his efforts at closer cooperation with Iran.
Al Qaeda-linked Sunni extremists, meanwhile, praised Saturday's attack on a moderate Sunni cleric who had recently spoken out against the terror network. Sheik Wathiq al-Obeidi was seriously wounded and three relatives were killed.
The Al Qaeda front group the Islamic State of Iraq did not officially claim the attack, but Web sites it generally uses to put out messages said it had been carried out by its militants.
Al-Obeidi was one of two Sunni leaders who took public stances against Al Qaeda in Iraq to be attacked Saturday, in a sign the terror network may ramp up retaliation against local chiefs who oppose it.
A local tribal leader in Albu Khalifa, a village west of Baghdad -- Sheik Fawaq Sadda' al-Khalifawi who had recently joined the anti-Al Qaeda alliance in Anbar province -- was gunned down by militants who broke into his home late Saturday, police said.
The United States has pointed to an anti-Al Qaeda alliance of local Sunni leaders as a sign of turnaround, but the attacks showed the high risks local leaders face by joining.
A powerful roadside bomb also killed the governor and police chief of a southern province that has been torn by fierce fighting between Shiite factions. Al-Maliki ordered an investigation and urged residents to show restraint and not launch reprisals.
In other violence, gunmen ambushed a police patrol southwest of the northern city of Kirkuk, killing three officers and wounding another, police Brig. Gen. Sarhat Qadir said.