At least 80 people were killed or found dead across Iraq on Monday, including 33 who were killed in a bomb attack in the Shiite neighborhood of Sadr City in Baghdad. The military said two U.S. servicemen were killed in separate incidents.

In an unannounced visit to Baghdad, U.S. National Security Adviser Stephen Hadley met with Prime Minister Nouri al-Maliki and his Iraqi counterpart to discuss military and political coordination.

A government official said Hadley was accompanied in the talks by U.S. Ambassador Zalmay Khalilzad.

"This is a long planned trip to get a first hand report of the situation on the ground from the political, economic and security fronts," said Gordon Johndroe, spokesman for the National Security Council in Washington.

Johndroe said Hadley's trip was not announced in advance in keeping with security precautions taken for visits to Baghdad by senior U.S. officials.

The talks were held in the Green Zone offices of al-Maliki and Mouwafak al-Rubaie, Hadley's counterpart, to follow up on a decision late last week to form a joint commission to coordinate U.S.-Iraqi relations, especially military activity.

The commission was established in a video conference Saturday between U.S. President George W. Bush and al-Maliki, who has issued a series of critical statements about American policy in Iraq over the past week.

"The two sides discussed the work of the committee which agreed to by between the prime minister and the American president and is designed to coordinate development of the Iraqi security forces, expedite military training, reconciliation among Iraqis and the war against terrorism," the government statement said.

The U.S. Embassy confirmed Hadley's visit, but gave few details.

"He is here as part of ongoing consultations with the Iraqi government," said an Embassy official, speaking on routine condition of anonymity.

The Embassy official said Haldey's visit had not been publicly announced in advance. He said he comment on when Hadley would return to Washington.

In other violence gunmen killed hard-line Sunni academic Essam al-Rawi, head of the University Professors Union, as he was leaving home. At least 156 university professors have been killed since the war began. Hundreds, possibly thousands, more are believed to have fled to neighboring countries, although Education Ministry spokesman Basil al-Khatib al-Khatib said he had no specific numbers on those who have left the country.

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The explosion in the sprawling Shiite slum of Sadr City tore through food stalls and kiosks at 6:15 a.m. (0315 GMT), cutting down men who gather there each morning hoping to be hired as construction workers. At least 59 people were wounded, police Maj. Hashim al-Yasiri said.

Sadr City, is a stronghold of the Mahdi Army loyal to radical Shiite cleric Muqtada al-Sadr, and has been the scene of repeated bomb attacks by suspected al-Qaida fighters seeking to incite Shiite revenge attacks and drag the country into full-blown civil war.

Ali Abdul-Ridha, injured on in the head and shoulders, said he was waiting for a job with his brother and about 100 others when he heard a massive explosion and "lost sight of everything."

He said the area had been exposed to attack because U.S. and Iraqi forces had driven into hiding Mahdi fighters who usually provide protection in the tumbledown district on the northeast extreme of Baghdad.

"That forced Mahdi Army members, who were patrolling the streets, to vanish," the 41-year-old Abdul-Ridha said from his bed in al-Sadr Hospital, his brother lying beside him asleep.

However, Falih Jabar, a 37-year old father of two boys, said the Mahdi Army was responsible for provoking extremists to attack civilians in the neighborhood of 2.5 million people.

"We are poor people just looking to make a living. We have nothing to do with any conflict," said Jabar, who suffered back wounds. "If (the extremists) have problems with the Mahdi Army, they must fight them, not us," he added.

Also among those killed were a woman selling tea and three children ranging in age from 10 to 15 years, said police Capt. Khadhim Abbas Hamza and Rahim Qassim Jassim, deputy head of the local health directorate.

The U.S. and Iraqi military have kept a tight cordon around Sadr City since a raid there last week in search of an alleged Shiite death squad leader, who was not found.

The last major bombing in Sadr City occurred on Sept. 23 when a bomb hidden in a barrel blew up a kerosene tanker and killed at least 35 people waiting to stock up on fuel for the Muslim holy month of Ramadan.

The U.S. military identified the latest casualties as a member of the 89th Military Police Brigade who was killed by small arms fire Monday in eastern Baghdad and a Marine assigned to Regimental Combat Team 5 who died in combat Sunday in restive Anbar province.

The latest deaths brought to 101 the number of American troops killed in Iraq this month.

The rebounding violence coincides with U.S. efforts to bring Sunni insurgents into a reconciliation process and an embarrassing public squabble with Prime Minister Nouri al-Maliki over a schedule for achieving breakthroughs in security and political goals.

Political tensions deepened further on Sunday when Vice President Tariq al-Hashemi, the country's ranking Sunni politician, threatened to resign if al-Maliki did not move swiftly to eradicate militias.

Mohammed Shaker, a key aide to al-Hashemi, said the threat was intended to send a message to the government over the rising sectarian violence. "We cannot live with this situation indefinitely," Shaker said.

He was joined on Monday by a Sunni ally, Adnan al-Dulaimi, who threatened to withdraw the Iraqi Accordance Front from parliament and the cabinet unless security improved.

"If current conditions continue, Iraq will be destroyed," al-Dulaimi said.

Al-Maliki depends heavily on the backing of a pair of Shiite political organizations and has resisted concerted American pressure to eradicate their private armies — al-Sadr's Mahdi Army and the Badr Brigade, the military wing of Iraq's most powerful Shiite political bloc, the Supreme Council for the Islamic Revolution in Iraq, or SCIRI.

The gunmen, especially those of the Mahdi Army, are deeply involved in the sectarian killings that have brutalized Iraqis in Baghdad and central Iraq for months.

The militias have also infiltrated the predominantly Shiite security forces, who suffered 300 deaths during Ramadan, mainly at the hands of Sunni insurgents but also in fighting between police and rival militia fighters.

At least 26 policemen were killed on Sunday, including 17 in one attack in the predominantly Shiite southern city of Basra. Gunmen dragged 15 policemen and two translators — instructors at the Basra police academy — off a bus at the edge of the city Sunday afternoon. Their bodies were found dumped throughout the city beginning about four hours later.

The worsening violence in Iraq has become a pivotal issue in U.S. midterm elections next month, placing strains on relations between Washington and al-Maliki's shaky Shiite-dominated government.

The prime minister last week issued a series of angry statements, denouncing U.S. plans for a timeline to measure progress as infringing on Iraqi sovereignty and complaining to U.S. President George W. Bush over what he saw as imperious treatment from U.S. Ambassador Zalmay Khalilzad.

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The complaint followed an announcement by the Afghan-born Khalilzad that al-Maliki had agreed to set a timeline for progress on security and political reforms — something the prime minister later denied.

In a TV interview on Sunday, Khalilzad said the squabble was a misunderstanding.

"That was a problem in how what I said was interpreted or translated to him and how it was played by some of the media here. What he understood as it was explained to him was that I had determined what issues and by when the Iraqis had to decide," the ambassador explained.

Saddam Hussein's chief lawyer walked out of court Monday after 12 of his requests were rejected, but the chief judge immediately appointed other attorneys to defend the deposed president.

The walkout came shortly after chief defense lawyer Khalil al-Dulaimi ended a monthlong boycott of the trial in which Saddam and six other defendants are charged with war crimes and crimes against humanity for a 1987-88 offensive against Iraq's Kurdish population.

Saddam already faces a possible death sentence in a separate case brought in connection with the killing of 158 Shiite villagers in Dujail after a 1982 assassination attempt against him. Iraqi court officials say a verdict in the first trial would definitely be handed down on Sunday, two days before the American election.

The Associated Press contributed to this report.