Thirty people were killed and 57 others wounded during an attack on refugees by largely Muslim Seleka militia in the north of Central African Republic on Wednesday, U.N. peacekeepers said on Thursday.

Avenging what they said was the recent murder of four young Muslims in the remote town of dirt roads and thatched mud huts, armed Seleka stabbed and hacked to death refugees who had fled previous violence in the region and set fire to buildings.

Central African Republic's U.N. peacekeeping mission MINUSCA, which has a base in the town, repelled the Seleka, killing 12, it said in a statement on Thursday. The other 18 killed were civilians.

"MINUSCA expresses its strong indignation and strong condemnation of the resurgence," the U.N. mission said, calling the Seleka response "disproportionate".

Central African Republic has been in chaos since early 2013 when the Seleka, which draws mostly from the country's minority Muslim population, toppled then-President Francois Bozize.

Militias representing the interests of the Christian majority responded by attacking Muslims and a fifth of the population fled their homes to escape the violence, leaving the isolated nation deeply divided along ethnic and religious lines.

The U.N. mission said that the Seleka targeted civilians, local authorities and non profit organizations in the town and had taken control of a school.

Three school teachers in training under a UNICEF program were killed in the attack, UNICEF said in a statement, condemning what it said was "unacceptable violence against civilians".

A U.N. investigation into the attack is underway.

MINUSCA, which has sought to keep the rival factions from fighting, called for "calm and restraint" on Thursday, though signs of tension remained. Refugees camped outside the U.N. base were chased away by Seleka who destroyed their temporary homes on Thursday, a Reuters witness said.