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American forces are carrying out their largest single military operation in Iraq since the end of major fighting, officials said Wednesday, with more than 4,000 soldiers surrounding a 30-square-mile peninsula just north of Baghdad said to harbor Baath Party loyalists planning and carrying out attacks on American troops.

Brief gun battles erupted when American forces surrounded the peninsula of rich green farmland, created by a broad curve in the Tigris River, early Monday, U.S. commanders said. Four Iraqis were killed, four Americans were wounded and 375 Iraqi men were detained.

Iraqi civilians bitterly complained that the operation was excessive. They said American soldiers handcuffed women and children, beat one man to death and allowed another to die of a heart attack.

American officials called the accusations “absolutely false.”

A pilotless drone, F-15 fighters and AC-130 combat planes circled overhead as dozens of armored vehicles and patrol boats cut off escape routes, showing the seriousness of the American effort to quell nascent armed resistance in Sunni-dominated areas north and west of Baghdad.

The area, known as the Sunni Triangle, was a bedrock of support for Saddam Hussein, a Sunni. It has been the center of a recent surge in attacks that have left 10 U.S. soldiers dead and dozens wounded in the past 15 days.

American officials said they had intelligence that senior Baath Party officials were hiding in the area. A released Iraqi detainee said he was asked about Ali Hasan al-Majid, a senior Baath military commander known as “Chemical Ali” for his role in using chemical weapons against Iraqi Kurds.

U.S. military officials had speculated al-Majid was killed during bombing raids in April, but Defense Secretary Donald Rumsfeld said last week that he might still be alive.

American officials said a major general and a colonel were detained along with 40 to 50 suspected fighters.

Col. Frederick Rudesheim, the commander of the operation that involved soldiers from the 3rd and 4th Infantry Divisions and paratroopers from the 173rd Airborne Brigade, said senior Baath officials were not the primary target.

Gauging the intensity of the surge in attacks has been difficult. U.S. military officials disclose the deaths of American soldiers in Iraq but do not routinely publicize every attack.

Military officials declined a request this week to produce figures totaling the number of attacks on Americans forces over the past six weeks.

But conversations with soldiers in the area, a prosperous region where the Tigris creates an island of green in a sea of brown desert, suggested that the level of skirmishes north of Baghdad has been intense. They said convoys were routinely fired on at night.

Residents complained Wednesday that American soldiers broke windows during searches and roughed-up male detainees.

Relatives of Jassem Rumyad, 52, accused U.S. soldiers of preventing them from giving medication to him before he collapsed and died of a heart attack.

Rumyad’s 80-old mother, Hella Khalif, said the soldiers handcuffed and gagged her when she and Rumyad’s wife and daughter shouted that he needed his heart medication.

“They put tape over my mouth,” she said.

American officials said the account was false and that they allowed the women to give Rumyad his medication before he died.

But one U.S. officer involved in the operation said soldiers in one location did handcuff women and children. The officer said he immediately ordered the handcuffs removed.

A second family accused American soldiers of beating to death Mehedi Ali Jassem, 53, with their rifle butts and ransacking his house. They showed a bloodstained mattress that they said was covered with Jassem’s blood.

American commanders denied the charges and said Jassem had a cut on his head and his house had been damaged when they arrived to arrest him. They said the suspected army general stumbled out the door, collapsed and died, apparently of a heart attack.