At least 77 civilians have been killed in clashes with Burundi's security forces since the start of anti-government protests in April, ABC News quoted a rights activist as saying Friday.

Another 1,000 people have been arrested and dozens of prisoners tortured, Pierre Claver Mbonimpa, head of the Association for the Protection of Human Rights and Detained Persons, said.

Mbonimpa said his group has representatives across the nation that have been tallying the death toll as well as visiting with prisoners. He also said he had personally helped several protesters who suffered torture to get treatment.

A police spokesman, Pierre Nkurikiye, denied the torture allegations but didn't say how many people are in custody over protesting against a third term for President Pierre Nkurunziza.

The Red Cross in Burundi said that in the capital, Bujumbura, alone at least 24 civilians have been killed and 591 more wounded in unrest over Nkurunziza's bid to extend his time in office after serving the constitutionally-mandated two terms.

Bujumbura has been tense since April 26, when protests began after the ruling party nominated Nkurunziza as its candidate in elections now scheduled for July 15. Protesters say a third term would be unconstitutional.

More than 90,000 people have fled to neighboring countries amid unrest, many of them saying they had to flee because of the violent activities of a pro-government militia known as the Imbonerakure.