"It was serious fighting and 38 militiamen were killed," the source told Reuters. The clash came a day after a UN deadline expired for voluntary disarmament by militias, who have killed hundreds of civilians in the mineral-rich region.

Earlier, the UN mission in Congo said South African, Bangladeshi and Pakistani peacekeepers exchanged fire with gunmen as they searched two militia camps 25 miles southwest of Bunia, capital of Ituri.

"The provisional information we have is that 18 militiamen were killed in today's operation," Kemal Saiki, a spokesman for the UN mission told Reuters.

"Our troops do not fire unless fired upon so the militia obviously shot first," he added.

The military source said many weapons and lots of ammunition were seized in the raid.

The UN mission had given militias in Ituri until April 1 to hand over their weapons and promised to strike at those who failed to comply in a lawless frontierland where hundreds of civilians have been killed this year.

Over 8,000 of the estimated 15,000 fighters in the region have so far surrendered their weapons.