UN Secretary General Ban Ki-moon on Saturday applauded the African Union's plan to establish a "prevention and protection mission" against ethnic and political violence in Burundi, saying the organization was ready to support its efforts.
Burundian President Pierre Nkurunziza has promised to fight any peacekeepers sent by the AU, but Ban said at the opening of an AU summit that the crisis demanded "serious and urgent" commitment from "all of us".
"In Burundi, I welcome your proposal to deploy human rights observers and to establish a prevention and protection mission," he told delegates in the Ethiopian capital, Addis Ababa.
"I applaud you for taking collective responsibility and acting decisively. The United Nations stands ready to support your efforts."
The AU is expected to vote on a proposal to send 5,000 troops to Burundi at the two-day summit, where the official theme is human rights.
Nkurunziza discussed the proposal with a delegation of the UN Security Council in December, which backed the AU plan. However, he said the arrival of peacekeepers would violate Burundi's borders.
More than 400 Burundians have been killed since April in anti-government protests, attacks by armed groups and as a result of police repression, according to the UN.
Nkurunziza's announcement in April that he would seek a third term in office, despite a constitutional two-term limit, unleashed the wave of violence. The president won an election boycotted by the opposition in July.
Ban said leaders should never use "undemocratic constitutional changes and legal loopholes to cling to power".
"We have all seen the tragic consequences when they do," he said.
On Friday Amnesty International said satellite images, video footage and witness accounts indicate the existence of mass graves in and around the Burundian capital, Bujumbura.
"These images suggest a deliberate effort by the authorities to cover up the extent of the killings by their security forces and to prevent the full truth from coming out," said Muthoni Wanyeki, Amnesty's regional director for East Africa.
Amnesty quoted residents of pro-opposition Bujumbura neighborhoods as describing how police killed alleged government opponents and took the bodies to undisclosed locations in December.
The United States expressed its "deep alarm" over the allegations of mass graves as well as the reported arrests of independent foreign journalists in the country.