Police officers fired warning shots at the protesters, he added, but a bullet pierced a high-voltage cable which collapsed on protesters about 100 meters from the UN base.
"Four protesters were killed by electrocution," according to town hall spokesman Dominique Kalonzo.
The incident happened when groups of young people attempted to besiege the United Nations peacekeeping base in the town, in South Kivu province.
Adrien Byadunia, the head of local NGO New Civil Society, confirmed the death toll to AFP.
The deaths in South Kivu come after two days of anti-UN protests in neighbouring North Kivu province during which 15 people, three of them peacekeepers, had died.
Demonstrations against the UN mission in the DRC -- known as MONUSCO -- began in North Kivu's main city Goma on Monday when crowds stormed a military base and a supply centre, looting valuables.
Unrest quickly spread and on Tuesday, three UN peacekeepers were killed in an attack on their base in the town of Butembo, which is also in North Kivu.
Twelve protesters died, in addition to the peacekeepers, government spokesman Patrick Muyaya said during a televised news conference on Tuesday night, condemning the violence.
MONUSCO is one of the world's biggest peacekeeping operations. However, it has come under regular criticism in Congo's east for its perceived inability to stop armed conflict in the troubled region.
More than 120 armed groups roam mineral-rich eastern Congo, where millions of people have been displaced and civilian massacres are common.