U.N. investigators have found a mass grave in an army camp in Congo's eastern Ituri district holding around 30 victims, including women and children, who appeared to have been executed, a spokesman said on Friday.

"Our human rights division followed up on information it received and has confirmed a mass grave of about 30 people," Kemal Saiki, spokesman for the U.N. mission in Democratic Republic of Congo, told Reuters.

The discovery was announced at a time when tensions were high in the capital Kinshasa to the west, where a former rebel chief was refusing to accept provisional results showing President Jospeh Kabila had defeated him in an October 29 presidential election run-off.

Saiki said the military prosecutor was investigating the Ituri grave and two officers, a captain and a lieutenant, had been arrested so far.

The grave, located in the army camp at Bavi, 40 km (25 miles) south of the Ituri regional capital Bunia, seemed to be recent, according to the investigators.

They believed the victims had disappeared during army operations against militia in late August or early September. This meant the killings would have taken place after the July 30 first round of elections in the former Belgian colony.

"Apparently these people were executed, among them are women and children," Saiki said.

"There are witnesses who directly accuse the First Brigade, which is based there (in Ituri), of being responsible."

The First Brigade is one of several Congolese army brigades made up of fighters from a plethora of rebel and government factions who fought in Congo's 1998-2003 war.

The elections were Congo's first free polls in more than 40 years. They crowned a peace process that ended the war, which triggered a humanitarian catastrophe that has pushed the death toll to around 4 million. More than 1,000 Congolese still die every day from violence, hunger and disease.

ARMY ACCUSED OF ABUSE

The army has frequently been accused of human rights violations across Congo's east, where violence has continued despite the peace deal three years ago and the presence in the country of the world's biggest U.N. peacekeeping force.

Anneke Van Woudenberg, a Congo expert with Human Rights Watch, said her organization had documented some 70 killings or summary executions of civilians in Ituri over the last year.

She said civilians were often taken by the army for forced labor or because they were suspected of being militia.

"It is one of the most abusive operations I have seen the Congolese army involved in," she told Reuters.

In Kinshasa, Kabila has sent Congolese army troops onto the streets following a riot by supporters of Bemba, who has challenged the presidential run-off result in the Supreme Court.

The court was set on fire during the riot by followers of Bemba, a vice president in Kabila's transition government.

Kabila said on Wednesday he would use the army to move soldiers loyal to Bemba, estimated at around 600, from Kinshasa, unless U.N. peacekeepers did this in 48 hours.

A first group of around 50 Bemba fighters were moved out of the capital on Thursday, as foreign mediators worked to avoid a repeat of gunbattles between Kabila's and Bemba's forces which rocked Kinshasa in recent months.