A Zimbabwean and two Congolese were in the region investigating an area for de-mining, said UN Congo spokesman Sylvestre Kilolo.
They were preparing to return to Goma on Thursday when they were kidnapped, and their vehicle was left on the road, he said.
Congolese soldiers have been fighting in this region against Rwandan Hutu rebels, known by their French acronym FDLR. Eastern Congo has been plagued by a myriad of armed rebel groups since the Rwandan genocide.
The UN's effort to fight the FDLR has been complicated by the Congo government's selection of two Congolese generals to lead the mission. The UN said that it could not work with those generals because they are accused of human rights abuses.
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Congo's military has gone ahead on its own with operations against the FDLR.
The UN Security Council unanimously approved a resolution in late March that cuts the U.N. Peacekeeping force in Congo by 2,000.
In eastern Congo, Rwandan troops launched an incursion into the North Kivu province, officials said. About 300 Rwandan soldiers were eventually pushed back into Rwanda, government spokesman Lambert Mende said.