BAGHDAD, Iraq - More than 2,660 Iraqi civilians were killed in Baghdad in September, according to new Health Ministry figures - 400 more than the month before despite an intensified US-Iraqi sweep aimed at reining in violence.

An Iraqi policeman stands at the site of a roadside bomb explosion which was planted near the back gate of the Yarmouk Hospital in western Baghdad Wednesday Oct. 11, 2006, wounding three civilians. More than 2,660 Iraqi civilians were killed in Baghdad in September amid the wave of sectarian killings and insurgent attacks, an increase of 400 over the month before, according to figures from the Iraqi Health Ministry. [AP]

The numbers indicate how tough the vital battle to secure Baghdad has proven amid a wave of bloodshed this year, not only from Sunni Arab insurgents but also from Shiite and Sunni death squads who kidnap and kill members of the opposing sect.

So far, October has brought no relief. A US soldier died Wednesday from a roadside bomb while patrolling in Baghdad. That brought to 40 the number of Americans killed across Iraq the past 11 days - a pace not seen since the US attack on the insurgent stronghold of Fallujah in November 2004.

Three car bombs in different parts of Baghdad and attacks elsewhere in the country killed at least 14 Iraqis on Wednesday. Bodies of 11 suspected victims of sectarian slayings were found around the southern city of Kut, while police in the northern city of Mosul discovered the beheaded corpse of a priest.

No cumulative figures for Iraqi deaths in October have been released. But several times this month, police have reported finding 50 to 60 bodies dumped around Baghdad over a 24-hour period, suggesting the bloodshed has not waned.

The Health Ministry figures emerged as a controversial new study claimed the Iraqi death toll in the war since the US-led invasion in March 2003 is vastly higher than believed. The study, to be published Thursday by the British medical journal The Lancet, said more than 600,000 had been killed, more than 10 times most estimates.

President Bush dismissed the number as "not credible," and the Iraqi government called it "inflated" and "far from reality."

The wave of killings in Iraq this year has prompted US officials to warn of a change in American policy unless Prime Minister Nouri al-Maliki's government shows within a few months that it can rein in militias blamed for sectarian violence.

Since Aug. 7, thousands of US and Iraqi soldiers have been pursuing Operation Together Forward in Baghdad, moving from district to district and searching building by building to clear out weapons and hunt down militiamen and insurgents. They have seized more than 1,700 weapons and arrested more than 120 people. They have also staged raids on prominent militia figures.

But the numbers from the Iraqi Health Ministry suggested that by the end of September, the sweep had yet to slow the bloodshed.

A total of 2,667 civilians in Baghdad died violent deaths during September, two senior Health Ministry officials told The Associated Press this week, based on an official monthly report from the ministry to the Cabinet.

By comparison, 2,222 people died violently in August in Baghdad, according to a UN report published in September, which was also based on official statistics from the Health Ministry.

The two ministry officials said the UN number was accurate. They spoke on condition of anonymity because the government has issued orders that the death figures not be released.

The monthly figures include two categories: the number of bodies taken in at the city morgue to determine the cause of death and the number of violent deaths reported by hospitals.

Hospitals reported 1,196 fatalities from explosions, shootings and other attacks in September, and the morgue listed 1,471 people who died from violence.

Shiite and Sunni death squads are known to kidnap their victims, then dump their bodies - often bound and tortured. So many of the morgue's bodies were likely from sectarian killings, though they also would include victims of criminal kidnappings and murders.

Sectarian violence was sparked by the February bombing of a Shiite shrine in Samarra, north of Baghdad. Shiites, a chief target in three years of Sunni insurgent attacks, responded with attacks on Sunnis, starting a cycle of reprisal killings.

The deadliest month was July, when 3,590 people were killed across the country, according to the UN. The number killed countrywide fell in August to 3,009, which the UN said could be attributable to Operation Together Forward.

US troops have taken a heavy blow in the growing violence. In September, 71 Americans were killed - 28 in Baghdad - the second deadliest month this year after April, when 76 died. The number of US wounded in September was 776, the highest since the Fallujah siege.

On Tuesday, militiamen struck back at US troops, firing four mortar rounds at a base in southern Baghdad, hitting an ammunition dump. The resulting fire set off tank and artillery shells that exploded throughout the night, though there were no injuries.

The Islamic Army in Iraq, a Sunni insurgent group, claimed responsibility for the attack in a statement posted on the Internet.

"With the help of God, the mortar and rocket squads of the Islamic Army have shelled a U.S. Army base with two rockets and three mortar shells," said the statement posted on a Web site known to be used by insurgents.

The same Web site aired a 4-minute video later Wednesday showing huge balls of flames stretching into the sky, and a cloud of gray smoke billowing from the site. The sound of explosions is faintly audible on the video, and the tape appeared to be shot from a distance of at least several hundred meters. The footage was stamped with the emblem of the Islamic Army in Iraq. The authenticity of the statement and video could not be verified.

Iraq's Shiite-led parliament on Wednesday pushed through a law allowing the formation of federal regions despite Sunni Arab objections that will splinter the country and fuel sectarian violence.

Many in Iraq's Shiite majority want to form an autonomous region in their heartland of southern Iraq, mirroring the Kurdish self-rule area already in place in the north. Shiites defend a decentralized federal system as the only way to ensure Iraq's communities can live together in peace.

The constitution, passed in a referendum last year over overwhelming opposition from the Sunni Arab minority, enshrines federalism.

Sunnis, however, fear the new law will create sectarian mini-states, giving Shiites and Kurds control of the oil wealth of the south and north and leaving Sunnis in an impoverished central zone.

Critics also warn that moves toward federalism could push Sunnis to more violence in trying to stop it.

The new law says autonomous regions cannot be formed for another 18 months, a concession to Sunnis. But the Sunni Arab coalition and two Shiite parties that also oppose the measure tried to prevent a vote by boycotting the session in an unsuccessful effort to keep the 275-seat body from reaching the necessary 50 percent quorum.

"This is the beginning of the plan to divide Iraq," said Adnan al-Dulaimi, leader of the Sunni National Accordance Front. "We had hoped that the problems of sectarian violence be resolved. We hope there won't be an increase in violence."