In a church in Rwanda, sobs ring out and candles flicker as refugees from neighbouring Burundi mark a year since one of the deadliest episodes of violence in their crisis-wracked country.

Darcy, 32, is one of about 200 Burundians who gathered to commemorate those killed when an attack on military installations by gunmen opposed to President Pierre Nkurunziza lead to a violent crackdown by security forces against those seen as "enemies" of the state.

"They entered homes, killing anything that moved inside. They raped the women they found inside, even though they were state police, soldiers who should have protected the population," said Darcy, who fled Burundi two weeks after the violence of December 11 and 12 last year.

In the church, a weeping woman recounts how her brother was killed in the crackdown.

The rampage of violence in which several witnesses described door-to-door killings in opposition strongholds of the capital Bujumbura, left 87 dead according to the government.

The United Nations estimates the figure could be as high as 200.

"When you see someone you know dead, it is like a nightmare," said Carmel, 19, who fled Burundi with her family in October 2015.

Burundi was plunged into crisis in April 2015 when Nkurunziza decided to run for a third term in office, sparking a failed coup attempt and months of protests that led to a government crackdown, armed attacks and assassinations.

A September report by UN rights experts recounted spine-chilling cases of torture and horrific sexual violence, mass arrests and disappearances and warned that "the crime of genocide also looms large".

Burundi has a long history of violence between its Hutu and Tutsi communities, which led to a 12-year civil war that ended in 2006.

Bujumbura has reacted to the mounting criticism by cutting ties with the UN's main human rights body and pulling out of the International Criminal Court (ICC), while slamming a "foreign plot" to destabilise the country.

-'Forgotten' -

The latest effort to get peace talks off the ground ran into trouble on Friday when mediator Benjamin Mkapa -- a former Tanzanian president -- urged the opposition to focus on 2020 polls and not those in 2015, which he said had come to a "legitimate conclusion".

The main umbrella opposition movement, the National Council for the Restoration of Arusha Agreement and Rule of Law (CNARED) -- which is exiled in Brussels -- was furious and asked the United Nations to take over as mediator.

"It really hurts me. I think that the international community, the region, has forgotten Burundi," said former bank employee Serge Barahinduka, 52.

A Burundian journalist -- one of many forced into exile -- told AFP she fears that desperation may force some of her countrymen "to go and fight instead of dying of hunger here".