The U.S. military said Monday that a natural gas explosion was to blame for a series of blasts that killed 47 people in a predominantly Shiite neighborhood the night before. But residents and the Iraqi government insisted the destruction was caused by car bombs and a rocket barrage from a neighborhood where American forces operate.

U.S. ordnance teams went to the Zafraniyah neighborhood and found "no evidence" of anything other than a "significant gas explosion" Sunday night followed by subsequent blasts related to a gas leak, said the U.S. military spokesman, Maj. Gen. William B. Caldwell.

"If in fact there had been a hole in the ground, there would be some residue from a Katyusha rocket if one had been fired there," he told reporters.

Iraqi officials said the damage was caused by car bombs and a rocket barrage fired from Dora, a mostly Sunni district — evidence that sectarian violence roiling the capital shows no sign of stopping despite an additional 12,000 U.S. and Iraqi troops soldiers rushed in to enforce peace.

Dora is one of the areas where the United States has increased the number of its troops to control extremist activities.

Prime Minister Nouri al-Maliki's office said in a statement that the attack started with a number of Katyusha rockets falling on a building followed by a car bomb, more rockets on a post office, a motorcycle bomb near a public library and mortar rounds near an Armenian church.

The statement said 47 people were killed and 100 injured.

"The terrorists planned this ugly crime so that it would inflict maximum harm on innocent civilians, and this is proof of their deep-rooted hatred for Iraq and their attempt to incite sectarianism," al-Maliki said.

At the site, residents dug through wrecked buildings and swept glass off the streets Monday. Huge slabs of concrete that once were ceilings in an apartment building lay atop each other in a heap at one spot.

A middle-aged man in a bloodstained disdasha, the traditional Arab robe, wandered aimlessly, hitting his face with his hands in grief. Residents said his six children were crushed to death when his house collapsed.

"This is terrorism against the whole nation," said Ali al-Sayedi, a municipal council member.

A pedestrian bridge, ripped off its mooring, crushed a car underneath. The roof of a house displayed a wide hole, exposing the steel reinforcing rods bent inwards. The blackened wreckage of an overturned car lay nearby.

The explosions Sunday night reinforced worries about the Sunni-Shiite violence that American officials consider the greatest threat to Iraq's stability more than three years after the U.S.-led invasion toppled Saddam Hussein's regime.

On Sunday, U.S. and Iraqi soldiers began searching more than 4,000 homes in the Sunni neighborhood of Amariyah in Baghdad while conducting a similar operation simultaneously in the Shiite district of Shula, the U.S. command said.

Much of the violence has been blamed on Sunni insurgents and Shiite extremists, who have been waging retaliatory attacks since the bombing of a Shiite mosque on Feb. 22. The United Nations estimates nearly 6,000 Iraqis were killed in May and June.

Caldwell, the U.S. spokesman, said Shiite extremists here are receiving arms, munitions and training from Iran. But he added it is not clear if Iran's Shiite clergy-dominated government is involved.

"We know that some Shiite elements have been in Iran receiving training ... We do know that weapons have been provided and IED technology been made available to these extremist elements," he said, referring to "improvised explosive devices" — the homemade bombs that are widely used in the anti-U.S. insurgency and sectarian violence.

On Sunday, unidentified gunmen killed Col. Mahjoub Khalaf Ghulam, a commander in the Iraqi oil protection force, in Tikrit, 80 miles north of Baghdad, police said. More than 250 Oil Ministry officials, workers and oil security personnel have been assassinated since the fall of Saddam.

At least 10 other people were killed Monday in shootings and bombings across Iraq, including three blacksmiths shot by gunmen in the northern city of Mosul.

A prominent Sunni cleric, Ahmed Abdul Ghafour al-Samaraie, escaped assassination when gunmen fired on his convoy in north Baghdad. One bodyguard was wounded in an exchange of fire.

Al-Samarie heads the Sunni Endowment, the government agency that cares for Sunni mosques and shrines across the country.