Iraqi forces launched raids Saturday into an industrial zone in Fallujah where authorities fear Sunni insurgents could be seeking to regain footholds in areas they once controlled.
But the offensive into the district of factories and workshops found no clear evidence that Al Qaeda in Iraq or its allies had re-established a major presence in Fallujah, said the city's police chief, Col. Mahmoud al-Issawi.
He said police and military units found only small stockpiles of buried weapons and explosives. No arrests were made during the all-day sweep.
Security forces, however, have sharply stepped up their guard against possible return of extremist factions to areas that have been relatively calm.
Fallujah, about 40 miles west of Baghdad, was a hub for Al Qaeda in Iraq and other insurgent factions before they were mostly driven out by a Sunni tribal uprising and U.S.-led campaigns more than two years ago.
There are worrying signs of violence returning.
On Thursday, a homicide bomber struck an Iraqi military base in Habbaniyah near Fallujah. The blast injured at least 38 Iraqi soldiers — and was the fourth major attack against Iraqi security forces this month.
The industrial zone was once a center for insurgent bomb-making and rocket production. Streets were sealed off before Iraqi police and military units swept in, said al-Issawi.
In a separate operation, U.S. Marines joined Iraqi security forces in a hunt for weapons caches near Karmah village east of Fallujah, the U.S. military said.
In southern Iraq, Iraqi security forces said they captured four suspected insurgents from Saudi Arabia, including one described as the leader of an Al Qaeda cell.
The men were arrested in Basra province three days after crossing into Iraq across the Saudi border, said Maj. Gen. Adil Daham, chief of the Basra provincial police.
The alleged Al Qaeda operative, Ihssan Mijim Khudhir, and three others were found in an abandoned mud hut about 15 miles south of Basra, said Daham.
He gave no other details about their alleged insurgent activity.