BUNIA, Congo - For six days, two terrified United Nations military observers phoned their superiors - as many as four times a day - begging to be evacuated from their remote outpost in northeastern Congo.

They were receiving death threats, they said. They were alone and unarmed in Mongbwalu, a former gold-mining town ruled by the cannibalistic Lendu tribal militias. A U.N. helicopter from the town of Bunia could have retrieved them in 35 minutes.

But the United Nations, handcuffed by its own rules and bureaucracy, never sent a chopper. On May 18, 10 days after the two peacekeepers made their first distress call, the United Nations finally flew some armed peacekeepers to Mongbwalu.

They found the mutilated bodies of Maj. Safwat al Oran, 37, of Jordan, and Capt. Siddon Davis Banda, 29, of Malawi.

Their decomposed corpses had been tossed into a canal and covered with dirt, according to those who saw the bodies. They were shot in the eyes. Their stomachs were split open and their hearts and livers were missing. One man's brain was gone.

The murders laid bare the challenge of bringing peace to one of the world's complex and resilient wars and exposed the limits of the United Nation's efforts to do so.

The U.N. mission in Congo (MONUC) has been criticized by many, including some in its own rank-and-file, for being disorganized and naive. Now, its critics charge, it's also partly responsible for the deaths of the two observers.

"Why didn't they rescue them? They had armed troops here, who could have saved them," said one U.N. observer in Bunia, who spoke on condition of anonymity.

"They killed them."

Col. Daniel Vollot, the MONUC sector commander in Bunia, said all U.N. employees here work in dangerous, unpredictable conditions and that MONUC isn't responsible for the deaths of Banda and Oran.

"We can't feel guilty," said Vollot. "Certainly, if we had arrived two or three days before, they would be alive. It's difficult, but I don't feel guilty about that."

The murders were a serious setback to U.N. operations in Congo's Ituri province, where some 50,000 people have died in fighting between Hema and Lendu tribal armies since 1999. After the killings, the United Nations pulled out all its military observers and sent them to Bunia, Ituri's largest town.

Now little is known about what happens even a few miles outside Bunia. Aid workers and human rights observers fear that vast human rights abuses are taking place across Ituri province.

MONUC is "a long, bad story," said Francois Grignon, the Central Africa director for the International Crisis Group, a Brussels-based research agency.

Details of the killings in Mongbwalu - one of the most horrific acts of violence against U.N. employees in the international body's 58-year history - are still emerging. The U.N. is investigating what happened.

But in separate interviews with Knight Ridder, five U.N. military observers with knowledge of what happened to Oran and Banda said their murders could have been avoided. In fact, they said, only luck prevented tribal fighters from butchering more helpless military observers trapped in other remote areas.

All five spoke on condition of anonymity because they worried about the repercussions they could face from the United Nations and their own countries.

Vollot acknowledged that Oran and Banda for several days had asked U.N. officials in Kisangani to be pulled out of Mongbwalu.

When asked why U.N. troops weren't sent to pick up the two observers, Vollot said his command's Russian-made Mi-26 helicopters were piloted by civilians. The Russian and Ukrainian pilots were afraid to fly there, and the United Nations didn't want to put their lives at risk, Vollot said.

And under U.N. rules, the ruling Lendu militia had to give permission to land a helicopter in Mongbwalu. It also was unclear which Lendu militia was in charge of the town, he said.

So his soldiers had to wait for clearance from the Lendu chief, and only MONUC headquarters in Kinshasa, the capital, could authorize a rescue operation.

"These are the rules of the United Nations," said Vollot.

The question in many minds is this: Why were the observers sent in the first place?

For years, Mongbwalu was a volatile, violent place in the most volatile, violent province of Congo. Six Red Cross workers were brutally murdered in Ituri in 2001.

Neither Oran nor Banda spoke French, Swahili or any local language. There were no armed U.N. peacekeepers in the area, and the observers were sent with no weapons.

It was Oran's first mission. He had little experience in Africa, let alone in a complex conflict such as Congo where military allegiances often switch day to day, said those who knew him.

"They were so at risk. It was not prudent for two milobs (military observers) to be sent with no force protection to a place which was known to be violent for years," said Nigel Pearson, the medical coordinator in Bunia for Medair, a relief agency.

"It was naive of MONUC. They weren't fully aware of the complexities of the situation."

The U.N. military observers agree. Several were sent in teams of four to other remote parts of Ituri at the same time as Oran and Banda in April. They were urged to go quickly with little preparation, they said. And after they arrived they received little attention from MONUC officials, they said.

"After we got there, they forgot us. Nobody told us what we had to do there," said another U.N. military observer. "I didn't even know which group was Hema and which was Lendu."

At the time, MONUC needed to have a strong presence in Ituri, said the observers. The Ugandan army, which occupied the province, was leaving in accordance with a multinational peace pact. MONUC was expected to fill the security vacuum.

"The U.N. was very pressured to find a solution to the Congo war," said a third U.N. military observer. "They sent observers too soon to a situation where we can't do our work."

On May 8, that became clear. With the Ugandans gone, clashes between Hema and Lendu militias had broken out all over the province. Oran and Banda called MONUC's offices in Kisangani asking to be evacuated, said a fourth U.N. military observer.

But it was unclear who was responsible for the observers. For the next four days, phone calls were exchanged among Kisangani, Bunia and Kinshasa about getting clearance to evacuate Oran and Banda.

"There was a lot of confusion," said the U.N. military observer.

Meanwhile, other U.N. military observers in other parts of Ituri also wanted to be evacuated. Many had to wait several days, too. Some ended up escaping on their own across the Ugandan border. Lendu militias intimidated other observers for days and accused them of spying for the Hemas.

In one instance, an observer had a gun pointed at his head. Armed fighters surrounded other observers, threatening to kill them.

"What happened to the two observers could have happened to me," said one observer, shaking his head.

The last telephone call from Oran and Banda was on May 13.

That was the day the United Nations believes they were killed.

"Everyone is to blame, starting from the guy who planned the operation," said the fourth U.N. military observer.

On Wednesday, MONUC held a memorial service for Oran and Banda in Kinshasa. Senior representatives of all 15 members of the U.N. Security Council, who are here on a fact-finding mission, attended the ceremony.