BUKAVU, May 29: UN peacekeeping troops moved on Saturday to secure the eastern Bukavu region in the Democratic Republic of Congo after three days of clashes and the killing of a UN military observer, UN officials said.

The observer from MONUC, the UN mission to the war-ravaged country, was shot dead overnight by gunmen who attacked him and two colleagues at Kalehe, some 40 kilometres north of Bukavu, near the Rwandan border.

Another observer was slightly wounded in the attack, the MONUC spokesman in Bukavu, Sebastien Lapierre, said, while the third, who had disappeared, was found to have been "just hiding and is safe and sound".

"MONUC strongly condemns this cowardly and abominable act," the mission said in a statement, vowing to find and detain those responsible.

Lapierre said that a MONUC ultimatum for one of the belligerent parties to canton its soldiers was being obeyed, and that most of the fighters were back in their barracks. "A few arrests" had been made by peacekeepers, he said.

"Right now, almost all (of Jules) Mutebesi's men are in their barracks apart from a few more who will be arrested," Lapierre said.

The fighting in Bakavu, chief town of Sud-Kivu province, has mainly pitted DRC regular troops against dissident soldiers led by Colonel Jules Mutebesi, who was named deputy commander of the region after the war but was suspended in March.

However, hours after the UN ultimatum came into force, several of Mutebesi's armed men were seen by AFP patrolling a Bakavu district which borders neighbouring Rwanda.

Mutebesi, too, was in the city, and refused to say whether he would accept the terms of the UN ultimatum.

"Who am I supposed to turn myself into?" he said. "I am still in the army, I am not a rebel."

Mutebesi is a former rebel from the Rwanda-backed Congolese Rally for Democracy (RCD) and one of the many ex-insurgents who were taken into the army under a series of peace pacts to reunite the central African country after its devastating five-year war.-AFP