Four people have been killed and dozens wounded in Burundi when police opened fire on a group of demonstrators protesting against a controversial bid by President Pierre Nkurunziza for a third term in office, which the opposition says is unconstitutional.

The deaths, which leading human rights activist, Pierre-Claver Mbonimpa confirmed, brought the death toll in more than a week of protests to at least 13, including two soldiers and a policeman.

Violence broke out in the capital, Bujumbura, when security forces fired gunshots and hurled tear gas canisters to disperse the crowd. Police erected road blocks to keep demonstrators away.

Protesters threw rocks at the police officers in response, wounding a number of them.

About 600 people have been arrested during a week of demonstrations against the controversial bid.

Agathon Rwasa, the opposition leader of the National Liberation Forces, has urged his supporters to join the anti-government rallies in the country, and to demand resignation of the president.

Meanwhile, the former presidents, Sylvestre Ntibantunganya, Domitien Ndayizeye and Pierre Buyoya have thrown their weight behind the protesters, arguing that a third term for the 51-year-old Nkurunziza would be against the constitution.

The National Council for the Defense of Democracy – Forces for the Defense of Democracy, which is the ruling party in Burundi and known by its French acronym, CNDD-FDD, has designated Nkurunziza as its candidate for the June 26 presidential election.

Burundi’s opposition also argues that the bid runs against the Arusha Agreement that ended the civil war of 1993, which lasted about a dozen years and claimed the lives of over 250,000 people.

In October 1993, Melchior Ndadaye, the first democratically-elected president of Burundi who came from the Hutu ethnic group, was assassinated after only 100 days in office. The assassination triggered deadly ethnic violence between Hutus and Tutsis, another ethnic group in Burundi.

Under Burundi’s constitution, presidents are limited to serving only two full terms. Supporters of Nkurunziza argue that his first term does not count due to the fact that he was selected by the parliament at the time.