Deadly violence shatters Eid al-Adha calm in Iraq - A GI is killed in a suicide attack, and a car bomb targets liquor stores. American troops find a torture chamber.

It was one of three attacks nationwide that shattered what had been the peaceful start of the Muslim holiday of Eid al-Adha, which began Wednesday for Sunni Muslims. Shiites begin celebrating the four-day holiday today. The violence included a bombing in central Baghdad that targeted a row of liquor stores and, police said, killed three Iraqis.

The violence underscored what a U.S. official called the "great security threats" still looming in Iraq, threats further illustrated by two recent discoveries.

In Diyala province, north of Baghdad, Iraqi civilians tipped off U.S. forces to a gruesome torture chamber, with chains on the walls and ceilings and a bed on which chained victims apparently were subjected to electrical shocks.

And south of Baghdad, the U.S. military said it found an elaborate system of tunnels dug by insurgents along the Euphrates River. The militants apparently used the tunnels as hiding places and as positions from which to fire on U.S. forces. Soldiers from the Army's 3rd Infantry Division, which found the tunnel system, used two bombs to destroy it.

The discoveries occurred in areas still plagued by Sunni Arab insurgent activity blamed on the group Al Qaeda in Iraq. Troops came across the tunnel network Sunday during a search that also uncovered a cache of bomb-making equipment in Iskandariya, 25 miles south of Baghdad. The torture center was discovered in Muqdadiya, 60 miles northeast of Baghdad, after a tip from local Iraqis. The remains of 26 people also were discovered at the compound, which was uncovered during a series of operations this month.

A military statement said 24 insurgents were killed during the three-day mission.

"There are still great threats out there," said a U.S. Embassy official who asked not to be identified. "Each attack illustrates that."

The bloodiest attack Thursday occurred in Kanan, about 12 miles east of the Diyala provincial capital of Baqubah. The U.S. military said a bomber wearing an explosives vest approached a building where a local council meeting was about to take place. Several U.S. soldiers were standing outside the building, according to a military statement.