At least 100 rebels have been killed after a cross-border attack against the central African nation of Burundi from the Democratic Republic of Congo, a top military source told Agence France Presse Sunday.

A general in the Burundian army, speaking on condition that he not be named, said the attack by the unidentified rebel group had been defeated after five days of heavy fighting in the border area north of the capital Bujumbura.

At least 35 people are now confirmed to have been killed in clashes between Burundi's army and members of an unidentified rebel group near the Democratic Republic of Congo border, an official said Wednesday.

"We've so far recovered 34 bodies of attackers. On our side, we have lost one soldier," a top Burundian army official told Agence France-Presse, the day after the rebel group launched the attack on the central African nation.

At least eight fighters were killed on Tuesday in clashes between Burundian security forces and members of an unidentified armed group which crossed into the central African nation from the Democratic Republic of Congo, officials said.

Burundian officials and witnesses said the armed group crossed into Cibitoke province during the night, and that Burundian soldiers and police had been locked in battles against the group throughout the day.

Authorities in the central African nation of Burundi said Monday they had arrested the brother of a man who was killed in France after a suspected Islamist-motivated attack.

A spokesman for Burundi's National Intelligence Service said Brice Nzohabonayo was detained in the capital Bujumbura shortly after his brother Bertrand Nzohabonayo attacked a police station in the central French town of Joue-les-Tours.

Civil society activists in Burundi are facing an "unacceptable" and escalating levels of harassment when they question the government, the U.N. said Tuesday.

Michel Forst, U.N. Special Rapporteur for human rights defenders, said civil society activists and journalists face a "high number of cases of physical threats, anonymous phone calls, assaults, arbitrary arrests, and judicial harassment" ahead of elections next year.

The United Nations' top adviser on preventing genocide on Saturday appealed for dialogue and greater freedoms in Burundi, which he said needed to avert "the worst" ahead of elections next year.

Speaking at the seat of the U.N.-backed Rwandan genocide tribunal in Arusha, Tanzania, Adama Dieng said Burundi had the right to vote "in complete peace."

The United States on Thursday issued a stark travel warning for Burundi after threats by al-Shebab militants and imposed a de facto night-time curfew on U.S. government staff in the country.

The State Department warned all American citizens to avoid non-essential travel to the small, impoverished country, nestled in Africa's Great Lakes region.

Tanzania said Tuesday it will grant citizenship to some 200,000 refugees from neighboring Burundi, a move hailed by the U.N. refugee agency.

"Those to be granted citizenship are refugees who have stayed in Tanzania since 1972 and have voluntarily opted to stay in the country," Home Affairs Minister Mathias Chikawe told Agence France-Presse.

Burundi said Tuesday it was certain that bodies found floating in a lake on its border had floated downstream from neighboring Rwanda, despite repeated denials from Kigali.

The appearance of the corpses over the past several months have sparked concern in a region scarred by decades of unrest and serious rights abuses. Officials say six bodies were found, although fishermen have reported seeing as many as 10 times that number.

The United States has called on Burundi and Rwanda to conduct a "thorough and impartial" probe into the appearance of several corpses in a lake bordering the two central African nations.

Officials say a total of six bound and bagged bodies have turned up in Lake Rweru over the past two months, although fishermen have reported seeing as many as 10 times that number.