An Iraqi guerrilla ambush on a U.S. tank column north of Baghdad backfired on the attackers Friday, as the Americans quickly turned the tide and hunted down and killed many of the assailants.

U.S. Central Command (search) said 27 Iraqis had been killed. But Lt. Col. Andy Fowler, commander of the 37th Cavalry (search) in Balad, the scene of the attack, said that only seven Iraqis were killed.

Asked about the Central Command reports of 27 killed, he said, "Those were the initial reports." He did not offer a further explanation for the discrepancy.

Fowler said the Iraqis attacked the tank column after a bomb or mine exploded in the street. The U.S. forces then pursued the attackers through a field.

There were no U.S. casualties, Fowler said.

The skirmish was part of the continuing, four-day-old "Operation Peninsula Strike (search)," intended to root out and destroy Saddam loyalists and Baath Party (search) fighters who have been harassing coalition forces. About 100 Iraqi fighters have been killed in four days of fighting, the U.S. military said.

In other developments, Air Force Gen. Richard B. Myers said U.S. forces were sifting through intelligence that "foreign fighters" may have been at an alleged terrorist training camp northwest of Baghdad bombed early Thursday by U.S. forces.

In Washington on Friday, a senior Pentagon official, speaking on condition of anonymity, said about 70 opposition fighters were killed in Thursday's attack on the training camp — most apparently non-Iraqis from other countries in the region.

If confirmed, it would be the first indication since the war's end that non-Iraqi volunteers were still in the country.

Separately, U.S. troops acting on an intelligence tip arrested 74 people described as sympathizers of the Al Qaeda terrorist network in a raid Thursday near the northern city of Kirkuk (search), said the U.S. Central Command.

Friday's ambush began when what Central Command called  an "organized group" ambushed a U.S. tank patrol with rocket propelled grenades in Balad, on the main north-south highway about 35 miles from the capital. The statement made no mention of U.S. casualties.

The patrol returned fire and killed four of the assailants in the initial gunbattle, the military said.

As the rest of the attackers fled, Apache helicopters joined the chase along with tanks and Bradley fighting vehicles (search), killing more assailants. The statement did not say whether any escaped.

Witnesses said the attackers rushed the tank column from a thicket of reeds near sunflower fields on an isolated rural road a few miles south of Balad.

Bassem Abdul Rahim, a 22-year-old farmer, said he was hiding with his family in his house about 150 yards away when he heard the shooting and saw flashes of gunfire. After the clash, the Americans took away the bodies, he said.

The tank patrol was from the Army's 4th Infantry Division, based in Fort Hood, Texas.

American warplanes bombed the alleged training facility 90 miles northwest of Baghdad on Thursday, looking for members of the now-banned Baath Party, Iraqi paramilitary groups and "other subversive elements," said a military statement.

A fierce ground battle followed the air strike in which the Iraqi forces suffered heavy casualties. One American soldier was wounded, said the Central Command.

"It was a tough fight. They were well-trained or well-equipped, and clearly well prepared for this, for the fight they had," Myers said at a Washington briefing on Thursday.

"There were many killed — a large number," Myers said.

"This is one of the many types of groups that we're going to have to confront, I think, for some time to come."

Before the war in March, Iraq claimed that thousands of Arab fighters poured into the country to resist the invasion. They provided some of the stiffest resistance once American forces entered Baghdad.

Since the war was declared over on May 1, about 40 Americans have been killed in ambushes and by sniper fire, mainly in the central area of Iraq where ousted President Saddam Hussein drew most of his support.

Six U.S. soldiers have been wounded in the past 24 hours in fighting in all of Iraq, Capt. John Morgan, spokesman in Baghdad for the Army's V Corps, said Friday.

U.S. military officials in Baghdad declined to give details of Friday's sweep north of Baghdad, saying the operations were ongoing and more fighting was possible.

Also on Thursday, Iraqi fighters shot down an Apache helicopter gunship — the first American aircraft downed by ground fire since Saddam's ouster two months ago — and a U.S. F-16 fighter-bomber crashed Thursday. The crews of the aircraft were rescued unharmed.

Earlier this week, U.S. forces launched a sweep through towns of the so-called "Sunni triangle" north of and west of Baghdad in central Iraq and marked at its top by Tikrit, Saddam's hometown.

Coalition forces did not give a total of Iraqi casualties in the operation, but said about 400 Iraqis have been arrested and many were being interrogated. No Americans have been killed, said Sgt. Forest Geary of the U.S. Army's 3rd Infantry Division.

Hundreds of U.S. troops moved in hard and fast through the area, centered on the town of Duluiyah 30 miles north of Baghdad. With helicopters whirring overhead and tanks offering cover, they kicked down doors and pulled out residents, looking for snipers who had harassed them for weeks from the shelter of thick woods.

"During the day, the people are calm and friendly, but at night they've been ambushing us," said Geary.

The aggressive raids angered people in Duluiyah, who complained of needlessly heavy-handed tactics by the Americans. One man said his 6-year-old son was handcuffed.

In a mourner's tent on a side street of the mostly shuttered town, Abid Ali Jassem al-Juburi, a former general in Saddam's army, said he was grieving for his brother and cousin who died early in the U.S. operation.

"My brother was beaten, hit in the face and was killed," he said, adding that U.S. troops took away medicine his family was bringing for a cousin who had suffered a heart attack "and smashed it under their feet."

Another resident, Ammar Salim, said 31 members of his family, males aged 13 to 70, were detained. "There was no reason for them to be arrested. They did nothing," he said. "They [U.S. forces] destroyed all our furniture, all our belongings."

Specialist Chris Rossi, of the 173rd Airborne Brigade, manning a checkpoint on the Tigris River, was unapologetic.

"We're just not taking any chances," he said. "My life's in danger so I'm going to approach them [the Iraqis] as hostile. And until I'm proved otherwise, that's the way I'm going to approach it."

As part of the effort to root out militants, the American civilian administrator of Iraq, L. Paul Bremer, on Thursday banned gatherings, pronouncements or publications that incite disorder or violence against the U.S.-led occupation forces, or the return of the Baath Party.

U.S. military officials also said two Iraqi prisoners were shot trying to escape from a camp Thursday. One of the men later died of his wounds and the other was recaptured, U.S. Central Command said.

The United States is holding more than 2,000 Iraqis, including more than half of the 55 Iraqi most-wanted by Washington.

Fox News' Greg Jarrett and The Associated Press contributed to this report.