Burundi’s main opposition party, the National Congress for Liberty (CNL), says about 10 of its members have been killed and 200 others jailed ahead of next month’s general elections.
Party spokesman Térence Manirambona told journalists in the main city of Bujumbura that political intolerance and violence against their members had intensified.
Five candidates, all men, are standing to replace President Pierre Nkurunziza, who has been in power since 2005.
The CNL’s Agathon Rwasa, a long time opponent of Mr Nkurunziza, is the main challenger to the ruling CNDD-FDD party’s candidate Maj Gen Evariste Ndayishimiye.
The CNL spokesman accused the ruling party’s youth wing, Imbonerakure, along with police and intelligence officers, of being behind the crackdown.
A ruling party spokesperson recently told the BBC that the CNDD-FDD could not comment as it was not the body to deal with such claims.
The government has previously rejected similar allegations of human rights abuses ahead of the 20 May vote.
On Wednesday, during a the UN Security Council session about the Great Lakes region, representatives from France, the UK and the US expressed concern about such reports.
US envoy Kelly Craft said her government’s message to Burundi’s was to organise “inclusive, peaceful, transparent and credible elections that would reflect the will of the Burundian people”.Article