NAIROBI — Rebel forces in Congo seized control Tuesday of Goma, a strategic provincial capital in the nation’s resource-rich east, despite the presence of UN peacekeepers in the area. The takeover sent tens of thousands fleeing and triggered fears of a regional conflict, according to officials and witnesses.

‘‘The atmosphere in the city is tense, people are worried,’’ Grace Tang, head of mission in Goma for the aid group Doctors Without Borders, said in a statement before the takeover. ‘‘The fighting that for months has forced hundreds of thousands to flee their homes elsewhere in the region has now reached Goma’s doorstep.’’