Kinshasa, Congo ? Congolese troops rescued four electoral workers from their militia captors in a raid that set off a battle that killed dozens of militiamen and one soldier, officials said Wednesday.

Mayi-Mayi fighters had kidnapped the officials Oct. 23 at Burondo in North Kivu province in northeastern Congo, and the army freed them late Sunday, military spokesman Jean-Willy Mutombo told The Associated Press.

“Some 40 Mayi-Mayi militiamen were killed by the army,” Mutombo said. “One soldier was killed and three others injured.”

A spokesman for a United Nations peacekeeping force, Col. Thierry Provendier, confirmed the rescue.

An extensive campaign is under way to register voters for Congo’s first presidential election in 45 years. It is due to be held by June under a peace accord that ended a ruinous 1998-2002 civil war that killed an estimated 4 million people.

Backed by U.N. peacekeepers, a transitional government formed after the accord is struggling to gain control over Congo’s east, which was formerly held by rebel groups whose leaders have been given top positions in the regime.