The US says violence has increased in the past two weeks and coincides with Ramadan.

Figures released on Thursday showed 40,000 families claimed assistance as refugees in the past seven months, up from 27,000 in July, but the statistics do not include an unknown number of Iraqis who have moved home but not claimed aid.

Sattar Nowruz, a spokesman for the migration ministry, said: "The reason for this increase is that the security situation in some provinces has deteriorated considerably, forcing people to leave their homes in fear for their lives."

Meanwhile, acts of sectarian violence continued to claim lives in Baghdad where police said they had found the bound bodies of 40 victims bearing signs of torture.

Multiple explosions

A car bomb and a roadside bomb exploded in quick succession in the Saadoun district of central Baghdad on Thursday, killing four people and wounding 38, police said. At least five other bombs went off in the capital, killing at least three and wounding 30.

Mortar rounds landed on a district in the southwest of the capital killing four. Bombs also exploded in the cities of Mosul and Numaniya.

US commanders have focused security efforts on Baghdad over the past two months and say they have managed to reduce the number of sectarian death squad killings in the scattered neighbourhoods they have targeted.

But the killers seem to have moved to other neighbourhoods and violence has not subsided in the city as a whole.

Death squads were returning to one of the areas the Americans had cleared, Ghazaliya, because police were allowing the killers back in, said a senior US military official who wished to remain anonymous.

Death squads

"We would ascribe that to probably some measure of some element in MoI facilitating the re-entry of folks into the area," said the official, referring to the interior ministry which oversees the police.

He described a surge in death squad killings since February by militants within the Jaish al-Mahdi (al-Mahdi Army) loyal to Muqtada al-Sadr, including some who had become "rogue" and were no longer under al-Sadr's control.

The death squads have been seeking out victims using lists of targets and placing them before religious leaders who sanction the killings, he said, giving one of the most detailed descriptions of US intelligence on the violence.

Since June they have carried out mass kidnappings, often of dozens of people stopped at a roadblock and separated out by their religion. They are held, tortured and killed, the officer said.