Police in Burundi have arrested a man for killing and raping three elderly Italian nuns murdered in twin attacks in their convent, the police spokesman said Tuesday.

"The suspected murderer of the three sisters is in our hands," Colonel Helmegilde Harimenshi said, adding the suspect had "confessed".

Three elderly Italian nuns were sexually assaulted and murdered in twin attacks in their convent in the capital of Burundi, police said Monday as a hunt was launched for their killers.

Lawyers in Burundi called Tuesday for an opposition leader to be jailed for five years for accusing the ruling party of preparing a "genocide."

Leonce Ngendakumana, president of the main coalition opposition party, is accused of making "damaging allegations, false accusations and racist incitement," in a letter he penned in February to U.N. chief Ban Ki-moon.

Fishermen in Burundi have found several corpses with limbs bound or stuffed in sacks, floating in a lake bordering Rwanda, government officials said Tuesday.

Some 40 bodies have been found in the lake since July, according to fisherman in the Burundian town of Giteranyi, the president of their association Sadiki Nyandwyi told Agence France Presse by telephone.

Belgian authorities have released a prominent Burundian opposition leader who had been detained at the airport last week while he was on route to Italy.

Alexis Sinduhije, a former journalist, activist and leader of the Movement for Solidarity and Development (MSD), was allowed to leave the airport detention center on Tuesday following a Belgian court decision to suspend his arrest.

The United Nations expressed "regret" over Burundi's decision Thursday to throw a senior U.N. official out of the country following a damning report alleging guns were being distributed ahead of elections.

The leaked internal U.N. report has raised fears of a return to civil war and the government has been warned about the risk, said Stephane Dujarric, a spokesman for U.N. Secretary General Ban Ki-moon.

Burundi's government has demanded the United Nations provide evidence or apologize after an alleged U.N. report claimed it was arming young supporters, amid renewed concerns over political violence.

Local media have been quoting from a puportedly leaked internal U.N. report that sounded the alarm over "allegations" that members of the Imbonerakure, the youth wing of Burundian President Pierre Nkurunziza's party, were being armed and trained in weapons use.

Burundi's government on Friday fiercely denied accusations that it was arming young supporters of the ruling party, amid renewed concerns over political violence in a nation still healing from decades of conflict.

Local media have been quoting from an alleged internal United Nations report that reportedly sounded the alarm over "allegations" that members of the Imbonerakure, the youth wing of Burundian President Pierre Nkurunziza's party, were being armed and trained in weapons use.

Burundi's foreign minister on Saturday said one of his country's diplomats had been expelled from South Africa, though the reason was not immediately clear.

The move comes after South Africa and Rwanda issued tit-for-tat diplomatic expulsions on Friday amid a row over the attempted assassination of an exiled Rwandan general in Johannesburg.

At least 51 people perished in flooding and landslides in a night of torrential rain in the Burundi capital that swept away hundreds of homes and cut off roads and power, officials said Monday.

Police in Bujumbura said the toll was the highest in living memory from a disaster caused by freak weather, with more than 100 people also injured.