At least 14 United Nations peacekeepers were killed in the restive Democratic Republic of Congo, officials said Friday, in the deadliest attack in the organisation's recent history.
UN Secretary General Antonio Guterres said the peacekeepers, who were from neighbouring Tanzania, were killed in the North Kivu province late Thursday, adding that around 40 were wounded, including several critically.
"I condemn this attack unequivocally. These deliberate attacks against UN peacekeepers are unacceptable and constitute a war crime," Guterres said in a statement.
Guterres put the death toll at "at least 12" but a statement from the UN's peacekeeping mission, MONUSCO, said later that 14 were killed.
DR Congo's huge eastern region has long been wracked by violence, but fighting between government soldiers and militia groups, as well as inter-ethnic clashes, has increased significantly this year.
North Kivu province, which borders Uganda and Rwanda, has seen a particular uptick in killings and kidnappings between rival ethnic groups.
The UN in October declared a level 3 emergency in DR Congo -- a status afforded to conflicts in Iraq, Syria and Yemen.
MONUSCO is believed to have been targeted on Thursday by the Ugandan Muslim rebel group ADF, one of several armed groups active in the North Kivu region, according to Congolese military sources.
Guterres said it was the worst attack on UN peacekeepers in the organisation's recent history.
"I call on the DRC authorities to investigate this incident and swiftly bring the perpetrators to justice," he said. "There must be no impunity for such assaults, here or anywhere else."
He said at least five Congolese soldiers were also believed to have been killed in Thursday's attack.
The medical evacuation of causalities is continuing, while military reinforcements have arrived on the scene, he said.
MONUSCO, a 18,000-member force, has suffered scores of attacks since its establishment in DR Congo, a vast, mineral-rich but chronically unstable nation home to myriad warring groups and ethnic groups.
The ADF was blamed for an ambush on UN peacekeepers in eastern DR Congo in October, which killed two peacekeepers and wounded 12.
The ADF has been accused by Kinshasa and the UN mission of killing more than 700 people in the Beni region since October 2014.
Human Rights Watch has documented more than 500 civilian deaths, at least 1,087 people kidnapped, and 11 reports of mass rape in North Kivu alone since June.
The UN estimates that more than four million people are internally displaced in DR Congo, and 922,000 people were forced to flee their homes last year -- more than in any other country.
Guterres warned in October against budget cuts to MONUSCO, the UN's largest and most expensive peacekeeping mission.
The UN's Under-Secretary-General for Peacekeeping, Jean-Pierre Lacroix, said on Twitter he was "outraged" by Thursday's violence.
The country has also faced violence after President Joseph Kabila, who was supposed to step down after his final term last December, pushed back a new vote until December 2018.
Kabila, in power since 2001, told the UN General Assembly in September that he was moving "towards credible, transparent and peaceful elections" but concerns persist that tensions over the vote will escalate into large-scale violence.
"This latest attack highlights the urgency of helping people in need and addressing the volatile situation," Guterres said.