Police found the bodies of 30 people on Friday, who bore signs of torture, the latest in a wave of sectarian killings sweeping through the Iraqi capital despite a month-long security crackdown.
A US Marine was killed on Friday in Anbar province, and an American soldier was killed Thursday evening by a roadside bomb northwest of Baghdad, the military said.
The soldier was the fifth to have died on Thursday, making it a particularly bloody day for US forces.
An Iraqi civilian was killed and five others were wounded when a gunman on top of an abandoned building opened fire in a Sunni Arab neighborhood Friday morning in central Baghdad, said police Lt Ahmed Mohammed Ali.
Both the US administration and military have said sectarian killings and violence are surging around Iraq, although the military has said the attacks are limited to parts of Baghdad not yet included in a security offensive that began on August 7.
A government imposed vehicle ban went into effect around Baghdad to prevent suicide car bombers and others attacking worshippers during Friday prayers.
The ban is applied every Friday. Violence has intensified over the past two days, with more than 130 people either killed by attacks or their bodies found dumped in the streets of Baghdad.
All the bodies found Friday also bore signs or torture and one that washed up on the banks of the Tigris had been dismembered.
The US Ambassador to the United Nations, John Bolton, told the Security Council that in the last three months "sectarian tensions, purposely incited by insurgents and extremists, increased ... resulting in increased killings, kidnappings, attacks on civilians, and increasing numbers of internally displaced persons."
He said late Thursday that ethnic and sectarian violence was "one of the most significant threats to security and stability in Iraq."
Over the last three months, Bolton said the average number of weekly attacks increased 15 percent and Iraqi casualties increased by 51 per cent compared to the previous three months.
The top UN envoy in Iraq, Ashraf Qazi, said that Iraq has become one of the most violent conflict areas in the world.
Maj Gen William B Caldwell, the US command's spokesman said the violence had intensified in areas that have not been reached by the security sweep known as Operation Together Forward and involving 12,000 US and Iraqi soldiers.
"The terrorists and death squads are clearly targeting civilians outside of the focus areas," Caldwell said Thursday.
In areas that have been part of the operation, US and Iraqi forces have cleared more than 52,000 buildings, found 32 weapon caches, detained 91 people and seized more than 1,200 weapons, Caldwell said.
One of the few positive developments for the US-led coalition and the national unity government was the reported killing of a senior member of Al-Qaeda in Iraq and the capture of another Al-Qaeda leader.
Iraq's Interior Ministry reported Thursday that Abu Jaafar al-Liby, who it described as either the second or third most important figure in Al-Qaeda in Iraq, was killed by police earlier this week.
Four other insurgents were killed and two were arrested in the raid, a ministry spokesman, Brig Abdul-Karim Khalaf, said.
Al-Liby was in charge of the Baghdad sector of Al-Qaeda in Iraq, Khalaf said.
He said two letters were found on his body — one addressed to Osama bin Laden and the other to Abu Ayyoub al-Masri, who is thought to be Al-Qaeda in Iraq's leader. Both letters pledged loyalty and promised more attacks, Khalaf said.
Caldwell said US military forces also had captured a senior Al-Qaeda figure and personal associate of the group's new leader. He was arrested along with 70 others Tuesday in a series of 12 raids, the US spokesman said.
The man, who was not identified, led assassination, kidnapping and bomb-making cells in Baghdad, and played a key role in Al-Qaeda's activities in Fallujah before it was attacked by US troops in November 2004, Caldwell said.
Shiite politicians, meanwhile, said they had made progress in trying to break a deadlock over legislation to establish autonomous regions as part of a federated Iraq.
Sunni Arabs oppose the bill, fearing it could split Iraq into three sectarian and ethnic cantons.
The proposed legislation, which could be introduced next week. Alliance leaders sent delegations to the Shiite holy city of Najaf to meet with radical Shiite cleric Muqtada al-Sadr and Grand Ayatollah Mohammed al-Yaqoubi, spiritual leader of the Fadhila party.