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-Qaida 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 65 kilometers west of Baghdad, was a hub for al-Qaida in Iraq and other insurgent factions before they were mostly driven out by a Sunni tribal uprising and US-led campaigns more than two years ago.