Violence raked Baghdad Monday as an Iraqi general took charge of the security operation in the capital and Iraqi police and soldiers manned new roadblocks — initial steps indicating the start of the long-anticipated joint operation with American forces to curb sectarian bloodshed.

At least 38 people died in bomb and mortar attacks across the city Monday, 15 of them as they waited to buy gasoline when two car bombs blew up in quick succession in south Baghdad. Seven people died after nightfall when four mortar shells rained down on a Shiite neighborhood in south Baghdad.

The violence was a sign of the difficulty facing the push that eventually will be able to call upon on as many as 90,000 American and Iraqi troops and police in a third attempt to calm the capital in nine months.

"It's going to be much more than this city has ever seen and it's going to be a rolling surge," Col. Douglass Heckman, the senior adviser to the 9th Iraqi Army Division, said Sunday.

Two past security operations in the capital over the past nine months — Operations Together Forward I and II — have failed and the United States blamed Iraqi authorities for failing to produce the number of troops promised.

Defense Secretary Robert Gates said last week that Iraqi troops who arrived to augment the newly assembled Baghdad force were only at about half the number promised.

A spokesman for the Sadr Movement, an important Shiite bloc in parliament, complained that the security crackdown had been too long in coming, especially given the series of bombings that have devastated mainly Shiite marketplaces over the past weeks.

At least 132 people died in a truck bombing Saturday in the Sadriyah market, the deadliest single bomb attack since the war began.

Falah Hassan, the Sadr bloc lawmaker and spokesman, said the delay "has negative consequences for the lives of the Iraqis."

"We demand that the plan be executed as soon as possible because the terrorists are going too far in their vicious attacks," Hassan said on behalf of the lawmakers loyal to the renegade anti-American cleric Muqtada al-Sadr.

The security sweep will be led by Lt. Gen. Abboud Gambar, who was named to the top position under pressure from the United States after it rejected Prime Minister Nouri al-Maliki's first choice — Lt. Gen. Mohan al-Freiji.

Gambar will have two Iraqi deputies, one on each side of the Tigris River that splits Baghdad north to south. The city was to be divided into nine districts, and there were to be as many as 600 U.S. forces in each district to back up Iraqi troops who will take the lead in the security drive.

The security drive, for which President Bush has dispatched 21,500 additional American forces, was seen by many as a last-chance effort to quell the sectarian violence ravaging the capital and surrounding regions.

As the operation slowly began, suspected Shiite militiamen burned down three houses in the largely Sunni al-Amil district in southwest Baghdad. Casualties were not known because police had blockaded the area.

The U.S. military reported the deaths of two American soldiers, both killed on Sunday.

Outside Baghdad, two key members of radical anti-American Shiite cleric Muqtada al-Sadr's political and military organization were killed, a sign that top ranks of the organization continue to come under attack from both Sunni insurgents and U.S. and Iraqi forces.

Ali Khazim, who ran al-Sadr's political organization in volatile Diyala province northeast of Baghdad, was killed Sunday by U.S. forces at his home in Howaider village, 12 miles east of Baqouba, Saleh al-Ageili, a spokesman for the Sadr Movement's parliamentary bloc, said on Monday. Provincial police confirmed al-Ageili's account.

The spokesman said Khazim was stabbed with a bayonet.

"What has happened to Khazim is part of the series of provocative acts by the occupation forces against the Sadr movement. The occupation forces know well who are the terrorists and their whereabouts, yet they are targeting our people," al-Ageili told The Associated Press.

The U.S. military said in a statement that Iraqi troops backed by Americans had shot and killed the leader of a rogue Mahdi Army group in Howaider. It did not name Khazim as the victim.

"The suspect is believed to have facilitated and directed numerous kidnappings, assassinations and other violence targeting Iraqi civilians and Iraqi Police. He is reportedly responsible for several attacks against Coalition and Iraqi Forces in the area," the military said.

The second Sadr organization official, Khalil al-Maliki, a key figure in the Mahdi Army militia in Basra, was killed by three gunmen in a drive-by shooting on Sunday. He survived an assassination attempt in the city last year.

As many as seven important members of the Sadr organization have been killed or captured in the past two months, at least three of them by U.S. forces, after the prime minister dropped his protection for the organization — a crucial backer in his rise to power.

On Sunday, an Interior Ministry official said about 1,000 Iraqis — including civilians, security forces and gunmen — had been killed in the last week alone. The official spoke on condition of anonymity because he was not authorized to release the figures.

Figures tallied by The Associated Press from police and government statements put the death toll from Jan. 28 until Saturday at 911. That included the 137 people killed in Saturday's truck bombing.