All the victims showed signs of torture, police Lt Thayer Mahmoud said. They were dumped in several neighbourhoods in both eastern and western Baghdad, he said.

The top US military spokesman in Iraq, Maj Gen William B. Caldwell, on Wednesday said murders and executions are currently the main cause of civilian deaths in Baghdad.

Much of the violence has been attributed to death squads, many of which are thought to be offshoots of mainly Shia militias.

Also Thursday, a pair of bombs exploded, one timed to go off after the other to ensure maximum casualties, in central Baghdad killing five people and wounding 15, medical sources said.

The Ibn al-Nafis hospital received five dead, including two police officers, and 15 wounded from a car bomb on Saadun street that was followed up by a second explosive device to harm those gathering at the site.

Elsewhere in Baghdad a suicide car bomber attacked an army post in the Shaab neighbourhood two soldiers and wounding 11 others, as well as one civilian, security officials said.

The suicide attack, which used a minibus packed with explosives, sent a plume of smoke visible across the city up into the air.

Another car bomb went off about half an hour later in the mixed Sunni-Shia Bayaa district in southwest Baghdad in a used-car lot, wounding two people.

A larger blast in the same neighbourhood on Wednesday killed five.

A National Police patrol was also targeted early on Thursday with a roadside bomb on the main city highway in east Baghdad which wounded three policemen.

The top US military spokesman in Iraq, Maj Gen William B Caldwell, says violence in the capital has spiked with the onset of the Muslim holy month of Ramadan, which officially began on Monday, and that suicide attacks were at their highest level ever.

"This has been a tough week," he said.

In other violence, a child was killed in the southern Baghdad neighbourhood of Dora when a mortar shell landed on a house, police said.

Seven policemen and three Iraqi Interior Ministry special forces were injured in three different bomb attacks in the capital.

Meanwhile Wednesday, American troops killed eight people four of them women after taking heavy fire during a raid on a suspected terrorist's house northeast of Baghdad, the US command said. But relatives of the dead disputed the US account, saying their family had nothing to do with any terrorist group.

In all, 23 people died violently around Iraq, including at least 10 killed in a shootout Wednesday night near a Sunni mosque in Hurriyah, a northern neighbourhood of Baghdad, police said. The US command also announced the deaths of a Marine and a US soldier, both killed in action Monday in Anbar province.

Outside the pockmarked house, which relatives said belonged to Mohammed Jassim, bullet casings littered the ground and blood stained the sand. Family members cried and consoled one another as the bodies of the women were taken away.

"This is an ugly criminal act by the US soldiers against Iraqi citizens," Manal Jassim, who lost her parents and other relatives in the attack, told Associated Press Television News.

Iraq's major Sunni clerical organisation, the Association of Muslim Scholars, condemned the raid as a "terrorist massacre."

The attack in Baqouba, 48km northeast of Baghdad, came as a new poll by the State Department and independent researchers indicated a strong majority of Iraqis want US-led military forces to withdraw immediately from the country. The poll, obtained by The Washington Post, showed, for example, that nearly three-quarters of Baghdad residents would feel safer if the US and other foreign forces left Iraq with 65 percent favouring an immediate pullout.

The top US military spokesman in Iraq, Maj. Gen. William B. Caldwell, told reporters there had been a spike in violence in Baghdad with the onset of the Muslim holy month of Ramadan, which officially began on Monday. Suicide attacks were at their highest level ever, he said without giving figures.

"We are seeing an increase in attacks, as anticipated. The terrorists and illegal armed groups are punching back in an effort to discredit the government of Iraq and more specifically the Baghdad security plan," Caldwell said. "This has been a tough week."

He said murders and executions are currently the No. 1 cause of civilian deaths in Baghdad, and operations against sectarian death squads have been stepped up.

Since mid-July, 29 death squad cell leaders and 254 members have been killed or captured, Caldwell said. There were 14 operations in the past week, resulting in two cell leaders and 42 members killed or captured.

"Iraqi security forces are making a concerted effort to defeat the insurgency and stop sectarian violence," Caldwell said. "Specifically Iraqi security forces are taking the fight to death squads within the Baghdad area."

On Wednesday alone, the bodies of 15 people found in various areas outside Baghdad were delivered to the morgue in Kut, 160km southeast of the capital. Most showed signs of torture and had their hands and legs bound; five were beheaded.

Operation Together Forward, a security drive to clear the capital neighbourhood by neighbourhood, was launched this summer after US generals warned sectarian violence was leading toward civil war. Sweeps have been started or completed in about half the neighbourhoods of the capital.

As of Sept. 25, 95,757 buildings had been cleared, 124 prisoners taken and 1,785 weapons seized in the operation. As part of the infrastructure rebuilding component, 6.6 million cubic feet of trash has been removed from the streets, Caldwell said.

There is a noticeable difference in the neighbourhoods that have been targeted, Caldwell said.

"When you look at the areas we've operated in, Dora used to be the highest amount of murders and executions within the entire city of Baghdad, and today now it's really probably the lowest level within the entire city because of the operations," he said.

In the southern city of Basra, British and Iraqi troops launched a security operation Wednesday aimed at rooting out corrupt police, pacifying the city and helping residents rebuild, the British military said.

Some 2,300 Iraqi army troops and 1,000 British soldiers started Operation Sinbad, with 2,000 more British troops conducting operations in the surrounding area, said British forces spokesman Maj. Charlie Burbridge. A key component of the operation is a crackdown on police corruption, he said.

Since January 2005, the predominantly Shia city has fallen under the influence of Shia militias, which have infiltrated police and local government institutions. In June, Prime Minister Nouri al-Maliki declared a state of emergency in Basra following a rise in violence among mostly Shia groups competing for power.

In Baghdad, meanwhile, the prime minister's military office said a leader of the militant 1920 Revolution Brigades was arrested Tuesday in the village of al-Jazira. The group is believed to be responsible for numerous attacks against US forces and a series of kidnappings.

Another leader of the group and seven aides were arrested Saturday in the same area, about 100km north of Baghdad. Authorities have not released the insurgents' names.

In the US-led raid in Baqouba, American soldiers came under fire when approaching the home of a suspect linked to the leaders of al-Qaeda in Iraq, the US command said in a statement.

US troops killed two terrorist suspects, then called in air strikes "due to the heavy volume of enemy fire from the target building," the military said. After the attack, they found the bodies of two more terror suspects and four women in the building. Three people were wounded, including two suspected terrorists who were detained, the military said.

The troops also found weapons and a global positioning system, the military said.

A family member said all eight people killed were relatives and disputed that they had any links to a terrorist group. "The Americans killed my relatives who had no guilt or relation with any group," Saleh Ali told The Associated Press.

"They were innocent people," said Manal Jassim, the homeowner's daughter. "We were sleeping when they entered our house at dawn. I found my father, mother, aunt and sister-in-law laying dead. We were an 11-member family. Eight were killed."

Caldwell said the American patrol had broadcast messages for people to leave the building peacefully but gunfire was the only response.

"It's extremely unfortunate whenever there's a loss of life. And nobody's quite sure what the connection was to all those people that were firing their weapons from that home. But it's unfortunate that anybody ever has to die," he said.