U.S. forces working Operation Peninsular Strike came by tanks, helicopters and boats to a town off the Tigris River northeast of Baghdad.
U.S. officials said at least twenty-seven Iraqis were killed after they tried to ambush a tank patrol.
Four thousand American soldiers came here to crush the increasingly deadly Iraqi resistance, which has left ten U.S. soldiers dead in the past two weeks.
"It was a decisive combat operation that was meant to first isolate the peninsula so that no one could enter or leave," said Col. Frederick Rudesheim, commander of the Third Brigade Combat team.
Countless Iraqi suspects were taken into custody, in a place described as full of Saddam Hussein's loyalists. Some Iraqis complained the troops came down too hard on civilians.
"My brother was killed," said one unidentified citizen.
Officials say they're after small and scattered groups of attacking Iraqis. In northwest Iraq, U.S. officials say at least seventy non-Iraqi fighters were killed after U.S. troops raided a militant camp.
"We continue to have to seek out, close with or apprehend or destroy them. That's going to take some time," said Lt. Gen. David McKiernan, commander of the Coalition Ground Forces.
U.S. strikes are the largest since the war. At least four U.S. troops were injured.