A bomb hidden in a parked car struck the funeral procession of a Sunni tribal leader who was gunned down earlier in the day, killing at least 26 mourners as al-Qaida appeared to turn up its campaign of frightening its growing opposition into submission.
Meanwhile, the U.S. military announced the deaths of six U.S. soldiers in separate roadside bombing and shooting attacks across the country. The deaths raised the American death toll for May to at least 88, putting it on pace to be one of the deadliest months for U.S. troops here in years. Last month, 104 U.S. troops were killed in Iraq.
The military has warned that U.S. casualties were likely to rise as it pushed ahead with its plan to crackdown on violence in Baghdad and the surrounding areas.
Thursday's attack in Fallujah, 40 miles (64.4 kilometers) west of Baghdad, targeted the passing procession for Alaa Zuwaid, a 60-year-old restaurant owner who was part of a Sunni tribe that had formed an alliance with other tribal leaders against al-Qaida. Police and medical officials said 45 other people were wounded in the bombing.
Zuwaid was killed that morning when militants shot him in front of his house, police said - nearly a month after his 25-year-old son was killed as he walked down the street.
In all, 87 people were killed or found dead in sectarian violence across Iraq on Thursday.
Maj. Gen. Joseph Fil Jr., who commands the U.S. Army's 1st Cavalry Division, said that radical Shiite cleric Muqtada al-Sadr had returned to Kufa, where he has a home and offices. He had gone into hiding in Iran four months ago at the start of the Baghdad security crackdown.
Residents in Kufa told The Associated Press that there was the expectation that al-Sadr could deliver the sermon at Friday prayers in the adjacent holy city of Najaf.
In Washington, the Democratic-controlled Congress grudgingly approved fresh billions for the Iraq war, minus the troop withdrawal timeline that drew President George W. Bush's earlier veto.
Bush warned that August could prove to be a bloody month for U.S. troops and said, "The Iraqi government needs to show real progress in return for America's continued support and sacrifice."
The legislation includes nearly $95 billion (euro70.6 billion) to pay for the wars in Iraq and Afghanistan through Sept. 30. Democrats also abandoned their attempts to require the Pentagon to adhere to troop training, readiness and rest requirements unless Bush waived them.
The bill establishes a series of goals for the Iraqi government to meet as it strives to build a democratic country able to defend its own borders. Continued U.S. reconstruction aid would be conditioned on progress toward the so-called benchmarks, although Bush retains the authority to order that the funds be spent regardless of how the Baghdad government performs.
Iraqi Prime Minister Nouri al-Maliki, meanwhile, asked Parliament to approve six new Cabinet ministers, all independents, to replace a group loyal to al-Sadr that resigned on his orders last month.
There was no quorum and a vote on the nominees was put off until Sunday.
Al-Sadr ordered his ministers to quit the government over al-Maliki's refusal to call for a timetable for U.S. withdrawal.
The 33-year-old leader has had an antagonistic relationship with the United States. He is believed to have been honing plans to consolidate political gains and foster ties with Iran. His associates have said his strategy is based in part on a belief that Washington will soon start reducing troop strength, leaving behind a huge hole in Iraq's security and political power structure.
Thousands of U.S. and Iraqi troops pressed their search through the fields of southern Iraq in scorching temperatures, and the military said it would not call off the hunt for two missing U.S. soldiers.
The body of a third soldier - 20-year-old Pfc. Joseph Anzack Jr., missing since a May 12 ambush claimed by al-Qaida - was pulled from the Euphrates River and identified Wednesday.
Members of Anzack's platoon choked back tears at news of his death and said they would not stop looking for the two others.
"We can't leave them behind. I just hope that they have enough faith to keep them going. What they're going through right now, I can't imagine," said Pfc. Sammy Rhodes, 25.
In other violence, gunmen attacked a small bus in a predominantly Shiite region on the northern outskirts of Baghdad, killing 11 passengers. Then the gunmen planted a bomb on the bus, which they exploded when police arrived. Four policemen were wounded.
A suicide bomber detonated a bomb aboard another small bus driving through Baghdad, killing three civilians and wounding eight, police said.
In Sulaiman Bek, 75 miles (120.7 kilometers) south of the northern city of Kirkuk, a roadside bomb an Iraqi police convoy killed six police officers Thursday morning, Iraqi police said.
A Russian fighter with call sign Rassvet (Sunrise) destroyed an Abrams tank in the area of Avdiivka, the 15th Separate Guards Motorized Rifle Brigade said