A fourth U.N. observer has died in volatile northeastern Congo, where rival tribal factions fight for control of the mineral-rich region. A Kenyan army officer, investigating reports of fighting between the rival Hema and Lendu tribal militias, was shot to death Thursday when his U.N. military convoy came under fire in Ituri province, said Leocadio Salmeron, spokesman for the world body's Congo mission. The officer, whose name was not released, was the fourth U.N. military observer to die in Ituri. Last May, an observer from Jordan and another from Malawi were captured, killed and mutilated by tribal fighters in a gold-mining town outside the provincial capital, Bunia. In April, a Russian U.N. military observer was killed and another injured when they drove over a land mine outside Bunia. Until recently, Hema and Lendu tribal fighters were locked in a bitter struggle for control of the province, but the main factions have now forged an alliance in the face of mounting pressure from a beefed-up U.N. force that is deploying to stabilize the troubled province. U.N. observers were visiting Katoto to probe reports of fighting in the area on Monday between rival factions of Hema militias, Salmeron said by phone from Bunia, the provincial capital. "The mission had just spent two hours on the ground, investigating the report of fighting and evaluating the situation by interviewing local residents," he said. Some 4,700 U.N. troops and unarmed military observers are in Ituri to stabilize the province and protect civilians, U.N. staff and aid workers from tribal fighting that has killed at least 50,000 people and forced some 500,000 to flee their homes since 1999. **PHOTO CAPTION*** Congo, Africa.