An internal report on the U.N. mission in Sudan admits "lessons" were learned from the way peacekeepers behaved during an attack on a disputed oil-rich town in which scores of civilians were killed.

The top U.S. envoy to Sudan Richard Williamson has accused U.N. peacekeepers in the region, known as UNMIS, of hiding in their barracks during the fighting in May instead of protecting Sudanese civilians in line with their mandate.

One part of the report on UNMIS, seen by Reuters on Thursday, says that the United Nations had identified several "lessons" to be taken from an assessment of the actions of the U.N. troops though it left out details of any mistakes made.

"A number of lessons learned were identified to inform future crisis response and force posture in UNMIS," it said.

U.N. special envoy for Sudan Ashraf Qazi rejected Williamson's comments, saying "UNMIS has neither the capacity nor the mandate to militarily intervene."

The violence in Sudan's Abyei region, which straddles the border between northern and semi-autonomous southern Sudan, killed dozens and forced about 50,000 people from their homes, igniting fears at the time that a new civil war could erupt between the north and south.

The new UNMIS report, which followed a U.N. Security Council demand for an investigation of what happened in Abyei in May, says "UNMIS sheltered and escorted to safety over 100 civilians who took refuge in the UNMIS compound."

But a Reuters reporter who was present at the UNMIS compound at the time of the attack saw things differently. According to the reporter, southern Sudanese soldiers left around 100 stranded civilians outside UNMIS' gates.

The reporter said UNMIS initially refused to allow the civilians inside the compound but the civilians eventually forced their way inside once a heavy firefight between northern and southern Sudanese soldiers began.

The U.N. peacekeeping department had no immediate comment.

Several U.N. diplomats told Reuters on condition of anonymity due to the sensitivity of the issue that they were concerned the report on UNMIS' actions during the Abyei attack could be a "whitewash" - in other words, an attempt to make it appear as if the Zambian peacekeepers had done nothing wrong.

PROTECTING CIVILIANS

The UNMIS report says a review of the force levels in Abyei will be part of a study of the military capabilities of UNMIS.

This is not the first time U.N. peacekeepers have been accused of leaving civilians in the lurch. Such allegations were widely raised about how peacekeepers behaved during the conflicts in Rwanda and the Balkans.

UNMIS is a 10,000-strong U.N. force, whose job it is to ensure that the north and south are complying with a 2005 peace agreement that ended two decades of civil war.

The 2005 peace deal left open the future status of Abyei, but leaders of northern and southern Sudan created a "road map" to defuse conflict and agreed to turn their border dispute over to an international court in The Hague for a final settlement.

According to the UNMIS Web site (www.unmis.org), U.N. peacekeepers in Sudan are authorized to protect civilians under threat of physical violence "without prejudice to the responsibility of the Sudanese government."

The report said UNMIS has a mandate to protect civilians under threat when possible but "responsibility for respecting the ceasefire lies squarely with the parties themselves."

Human Rights Watch said on Wednesday that tens of thousands of civilians driven from their homes in Abyei by the fighting in mid-May were still unable to return home two months after half the town was destroyed in fighting.

"Abyei can't wait," the rights group's Selena Brewer said, adding that the force in Abyei at the time of the attack was insufficient for a potential flashpoint like it. "UNMIS needs to deploy a much stronger unit there right now."