A statement said the attack blamed on Burundian rebels and a Congolese militia on Tuesday targeted a vehicle transporting members of a local educational group, Eben Ezer, at Fizi, in Sud-Kivu province.
At least two people were wounded.
The UN’s Office for Coordination of Humanitarian Affairs (OCHA) said it was the deadliest attack on aid workers ever recorded in the country and had left colleagues “very shocked”.
“It strengthens the feeling of insecurity which has reigned for several months in humanitarian organisations in the east of the country,” where both local and foreign insurgent groups wage war on each other and the civilian population.
Those responsible were said to be members of the Mai Mai Yakutumba militia and allied rebels of Burundi’s National Liberation Front.
OCHA said that nearly 25 incidents involving aid workers had been recorded since August in Nord-Kivu province and some 15 in neighbouring Sud-Kivu, and nearly 140 all told so far this year.
“These incidents range from hold-ups to hostage-taking and the hijacking of humanitarian vehicles to transport military equipment,” it said.
Former lawmaker Enock Ruberangabo, the national president of an association of Banyamulenges — ethnic Tutsis of Rwandan origin who live in Kivu — told AFP Tuesday’s assailants “clearly said they were looking for ‘Rwandans’, i.e. Banyamulenges”.
“They killed (them) one after the other,” he said, quoting two survivors and four people who were no Banyamulenge and had been released by the attackers.
Ruberangabo said the attack was to fan an “ethnic conflict at the local level”.
“We deeply regret this attack and all the others that hinder the work of humanitarian actors in DRC,” said Pierrette Vu Thi, interim coordinator of humanitarian activities in DR Congo, according to OCHA.
She called on the DR Congo government to immediately open an investigation as the protection of Congolese citizens and members of national and international organisations was the duty of the government.