Four people protesting against a United Nations peacekeeping mission were killed on Wednesday in the Congolese city of Uvira when troops fired warning shots which hit an electric cable that fell on the protesters.

The protests had mostly fizzled out on Wednesday in the cities of Goma and Butembo but had spread to Uvira, in South Kivu province, where crowds threw rocks at a MONUSCO compound.

"There was an isolated demonstration in Uvira. We had a tragedy because of the fall of an electric cable... indirectly related to the protest," South Kivu governor Theo Ngwabidje Kasi said.

"I have asked for investigations to know if the bullet was fired by MONUSCO or by our forces," he said, adding that preliminary information suggested it had come from within the MONUSCO base.

U.N. Secretary-General Antonio Guterres on Tuesday condemned the violence and called on the government to bring the perpetrators to justice.

The U.N. mission, which has around 12,400 troops in the country and costs more than $1 billion per year, has been in the process of gradually withdrawing for several years.

The U.N. children's agency said on Wednesday that many children had been manipulated into joining the protests and were exposed to violence.

Grant Leaity, UNICEF representative in the DRC, in a statement said, "UNICEF condemns the instrumentalization of children for political purposes and calls on authorities, members of civil society and parents to keep children away from protests in order to protect them."