Baghdad, Iraq ? In a well-publicized show of force, U.S. and Iraqi forces swept into the countryside north of the capital in 50 helicopters Thursday looking for insurgents in what the American military called its “largest air assault” in nearly three years.

The military said during the assault – Operation Swarmer – forces detained 41 people, found stolen uniforms and captured weapons including explosives used in making roadside bombs. It said the operation would continue over several days.

There was no bombing or firing from the air in the offensive northeast of Samarra, a town 60 miles north of Baghdad, the U.S. military said. All 50 aircraft were helicopters – Black Hawks, Apaches and Chinooks – used to ferry in and provide cover for the 1,450 Iraqi and U.S. troops.

Residents in the area reported a heavy U.S. and Iraqi troop presence and said large explosions could be heard in the distance.

Operation Swarmer came as the Bush administration was attempting to show critics at home and abroad that it is dealing effectively with Iraq’s insurgency and increasingly sectarian violence.

White House spokesman Scott McClellan denied the offensive was tied to the new campaign to change opinion about the war. “This was a decision made by our commanders,” he said, adding that President Bush was briefed but did not specifically authorize the operation.

The attack was launched as Iraq’s new parliament met briefly for the first time. Lawmakers took the oath but did no business and adjourned after just 40 minutes, unable to agree on a speaker, let alone a prime minister. The legislature set no date to meet again.

Still, the session marked a small step toward forming a unity government that the United States hopes will calm the insurgency and enable it to begin withdrawing American troops. U.S. military forces have been trying to build up the Iraqi army so that it can play a leading role in fighting the insurgents.

Thursday’s operation appeared concentrated near four villages – Jillam, Mamlaha, Banat Hassan and Bukaddou – about 20 miles north of Samarra.

The settlements are near the highway leading from Samarra to the city of Adwar, scene of repeated insurgent roadblocks and ambushes.

“Gunmen exist in this area, killing and kidnapping policemen, soldiers and civilians,” said Waqas al-Juwanya, a spokesman for provincial government’s joint coordination center in nearby Dowr.

Samarra, the largest city near the operation, was the site of a massive bombing against a Shiite shrine on Feb. 22 that touched off sectarian bloodshed that has killed more than 500 and injured hundreds more.

It is a key city in Salahuddin province, a major part of the so-called Sunni triangle where insurgents have been active since shortly after the U.S.-led invasion three years ago. Saddam Hussein was captured in the province, not far from its capital and his hometown, Tikrit.