Attackers in the Congo shot and hacked to death six workers of the International Committee of the Red Cross in the deadliest attack on the aid group in five years, international aid officials said Friday.

The dead in Thursday's assault were a Swiss nurse, a Colombian relief worker and four Congolese.

A Ugandan military patrol found the bodies by their two vehicles in rebel- and Ugandan-held northeast Congo, said Antoine Atawamba, spokesman for the organization in the Congo capital of Kinshasa.

Some of the victims had been shot; others were both shot and slashed with machetes, said Boni Mbaka, a U.N. official in the far northeast border town of Bunia who saw some of the bodies.

"It's very horrible. There were no survivors, [so] it's difficult to say what happened," Mbaka said.

The bodies were found about 40 miles north of Bunia. The teams had been heading to a remote health center with medicine, said Paul Castella, head of the ICRC delegation in Kinshasa.

Colleagues grew alarmed Thursday afternoon after losing what had been regular radio contact with the teams, and triggered the search, Red Cross officials said.

The killings took place in Ituri province, which is under the control of the Congolese Liberation Front, a Ugandan-backed rebel group led by Jean-Pierre Bemba.

The region has been plagued by fighting among Hema pastoralists and Lendu farmers for control of rich grasslands. Fighting had subsided in recent months following peace talks.

"We didn't consider that a particularly dangerous area," Castella said.

However, humanitarian groups in the area frequently face accusations by one group or the other of being biased.

The aid group immediately suspended operations in the area A decision would come later on whether to pull its staff -- roughly 20 expatriates and 200 Congolese -- out of east Congo.

"We would need to know more about the circumstances and motives behind the killings before we can evaluate what to do," spokeswoman Antonella Notari said in Geneva.

U.N. relief agencies and international nonprofit agencies based in eastern Congo were meeting late Friday to decide whether to continue humanitarian operations in the region, Alexandre Gashangi of the U.N. office for humanitarian affairs said.

"In the light of the horrific killings, it is highly unlikely that international relief organizations would want to continue operating in the area," he told the Associated Press.

The killings marked the worst single attack against the ICRC, a neutral Swiss-run humanitarian agency, since 1996, when six nurses were slaughtered in their sleep at a hospital in Chechnya. Three ICRC workers were killed in Burundi the same year.

Notari said the dead included a 36-year-old Swiss nurse, Rita Fox, and a 54-year-old Colombian relief worker, Julio Delgado.

The four Congolese staff were nurse Veronique Saro, 33; Unen Ufoirworth, 29, a staff member in charge of reuniting families separated by the fighting; and drivers Aduwe Boboli, 39, and Jean Molokabonge, 56.

They are responsible for food and nonfood aid to the many thousands of people displaced by the long-running turmoil in the area; giving medical assistance to hospitals; providing basic water services; and trying to trace and reunite families.

As usual, the workers had been traveling in vehicles marked with the Red Cross emblem, and without armed escort, the organization said.

The same day, five civilians and two others were killed in fighting between Bemba's rebels and local Mayi-Mayi fighters in the eastern city of Butembo, several days' drive to the south of Bunia.

MISNA, an Italian missionary news service, said fierce exchanges of gunfire in the city itself caused panic among the city's people.

Eastern Congo has seen some of the fiercest fighting in Congo's 2 1/2-year-old civil war, which has five foreign nations backing either the government or their favored rebel movements.

The war is blamed, indirectly, for more than 1 million deaths in the east alone, mostly among civilians cut off from food and medical care.

Ugandan forces, which are allied to rebels fighting Joseph Kabila's government in Kinshasa, nominally control Bunia, a trading town near the Ugandan border. It was the scene of bitter clashes between rival tribal warriors in January in which an estimated 200 people were killed.

"The ICRC expresses its heartfelt sympathy to the families of the deceased, who gave their lives for the ideal of solidarity with the victims of the conflict in the Democratic Republic of the Congo," said an ICRC statement.

"Profoundly grieved by this tragedy, it condemns in the strongest terms this attack and the flouting of the Red Cross emblem."