Car bombs triggered gas explosions in a Shiite neighborhood two days ago, the U.S. said Tuesday, acknowledging that the attack was due to a hostile act.

At least 63 Iraqis were killed and 140 wounded in the series of explosions Sunday night in Zafraniyah. Iraqi officials said the blasts were due to car bombs and a rocket attack from a Sunni neighborhood under U.S. control.

But U.S. military spokesman, Maj. Gen. William Caldwell, insisted Monday that American experts had concluded that there was "no evidence" of anything other than a "significant gas explosion."

That implied that the blast may not have been due to a hostile act.

However, a U.S. statement Tuesday said the blasts were triggered when two car bombs detonated near a residential building, "causing a gas explosion" that collapsed the structure.

It said the blast was among four car bombs that took place within a 30-minute period and within two miles of one another.

"Four buildings and 20 shops were destroyed," the statement said.

Iraq's Interior Ministry said the rocket and mortar attacks were unleashed from Dora, a Sunni neighborhood that U.S. troops have targeted in their security crackdown. A Sunni extremist group claimed responsibility for the blasts in a statement posted on the Internet.

On Monday, Interior Ministry spokesman Col. Saddoun Abu al-Ula said Iraqi experts had examined the area and concluded that rockets were also used in the attack. The U.S. statement made no mention of rockets.

"From the extent of the damage and some of the remains, it is clear that the explosions were caused by bombs and rockets," Abu al-Ula said. "What the Americans are saying is not correct. Maybe they are trying not to shoulder responsibility because the rockets were fired from Dora where there is heavy U.S. deployment."