The United Nations says at least 150 Congolese Tutsis have been killed in an overnight raid on a refugee camp in western Burundi. A Burundian Hutu rebel group has claimed responsibility, but survivors say the massacre was carried out by Rwandans, Congolese and Burundians.

The Tutsi victims, mostly women and children living in a refugee camp in Burundi, were killed in a raid by Hutu attackers wielding automatic rifles and machetes.

The refugees had fled to Gatumba refugee camp, near Burundi's border with neighboring Congo, because they had felt targeted in recent fighting in eastern Congo.

But protected by just 10 Burundian army soldiers, the civilians were killed as they slept or tried to escape by heavily armed men who witnesses say were barefoot and wore no uniforms.

Scores of others were injured, and the United Nations says that some of the survivors likely will die from their injuries.

According to reports, some of the refugees and much of the camp that housed up to 3,000 people were set afire in the attack. Visitors to the scene Saturday said they saw charred bodies and that other victims had been shot.

The Hutu Forces for National Liberation, a Burundian rebel group, has claimed responsibility for the attack, saying it occurred during an operation targeting the Burundian army.

But some witnesses said the attackers spoke several languages from the region, and that they came from Burundi, Rwanda and Congo.

Congolese Vice President Azarius Ruberwa, himself a Tutsi, had been in Burundi on Friday trying to encourage the refugees to return, insisting it was safe. On Saturday, he called the massacre an act of genocide, and warned that elements of Congo's newly reformed army had taken part.

Congo's transitional government is struggling to lead the huge African nation out of five years of war. But fighting in eastern Congo in June reignited the conflict, forced an estimated 30,000 Congolese Tutsis to flee into Burundi and threatened to bring down the peace process.

Because of the ethnic tensions still at play in the Great Lakes conflict, analysts fear this attack on the Congolese Tutsis may have more repercussions.

Rwanda's president, Paul Kagame, has condemned the attack, saying it proves that people in eastern Congo were being targeted because of their ethnic background.