Fourteen United Nations peacekeepers have been killed in clashes in the Democratic Republic of Congo, a UN official said yesterday-- the worst attack in the organisation's recent history.

UN Secretary General Antonio Guterres, who put the death toll at "at least 12" Tanzanian peacekeepers, said another 40 were wounded in the violence.

A UN official, who spoke anonymously, told AFP that 14 peacekeepers were killed.

The UN peacekeeping mission in the country, MONUSCO, is believed to have been targeted by Ugandan Muslim rebel group ADF, one of several armed groups active in the North Kivu region, according to Congolese military sources.

In a statement, Guterres said it was the worst attack on UN peacekeepers in the organisation's recent history.

"I condemn this attack unequivocally. These deliberate attacks against UN peacekeepers are unacceptable and constitute a war crime," Guterres said in a statement.

"I call on the DRC authorities to investigate this incident and swiftly bring the perpetrators to justice. There must be no impunity for such assaults, here or anywhere else."

Guterres said at least five Congolese soldiers were also killed in Thursday's attack.

The medical evacuation of causalities is ongoing, while military reinforcements have arrived on the scene.