Protesters in Burundi have clashed with police for a third day in fresh demonstrations against the president's bid for re-election for a third term.

At least six people have died since clashes broke out on Sunday after the ruling CNDD-FDD party, which has been accused of intimidating opponents, designated President Pierre Nkurunziza its candidate in the June 26 presidential election.

Three people were killed in clashes with the police and three others died of their injuries overnight, Alexis Manirakiza, spokesperson, told Associated Press news agency from Bujumbura, Burundi's capital.

He said seven others were wounded.

AFP news agency reported of a heavy police presence across Bujumbura, with crowds of a few hundred people broken up soon after they gathered and blocked from heading to the city centre.

The government has banned all protests and deployed large numbers of police and troops onto the streets, firing tear gas and water cannons, with hundreds of stone-throwing protesters arrested.

Some of those killed were shot at close range.

Bujumbura has been hit by protests since Sunday after the ruling party nominated Nkurunziza for another term, which many say is unconstitutional.

The president, a former rebel leader, has been in power since 2005.

Opposition figures and rights groups say his attempt to stay in power also goes against the peace deal that ended a 13-year civil war in 2006, in which hundreds of thousands were killed.

But his supporters say he is eligible to run again, as his first term in office was after he was elected by parliament - not directly by the people as the constitution states.

Burundi's constitution says the president "is elected by universal direct suffrage for a mandate of five years renewable one time," but Nkurunziza's supporters say he is eligible to serve a third term because he was first installed as president in 2005 by parliament to lead a transitional government, and not by a popular vote.

Those who oppose Nkurunziza, running for a third term include members of his own party, lawmakers, the clergy, student groups and civil society.

Activist jailed

On Monday, authorities arrested Pierre-Claver Mbonimpa, a human rights activist, and shut down the main independent radio station.

Mbonimpa's lawyer, Armel Niyongere, said he believed "the arrest is linked to his call for demonstrations".

An arrest warrant has also been issued for Vital Nshimirimana, head of a prominent NGO forum and leader of the campaign to block a third presidential term, sources told the AFP news agency.

Police have also confirmed the arrest of 320 demonstrators.

At least 15,000 Burundians have fled the country to neighbouring Rwanda in recent weeks, according to the UN refugee agency, which has warned that those numbers could rise.

Many are fleeing threats by the pro-government Imbonerakure, the youth wing of the ruling party. Rights groups allege that the group has been armed and trained over the past year in order to help Nkurunziza remain in office.

The EU said violence, arrests of human rights activists, restrictions on the media and an outflow of people into neighbouring countries had no place in an electoral process.

After Sunday's protest deaths, the African Union appealed to Burundi's government to "exercise the highest restraint and protect the population".

UN rights chief Zeid Ra'ad Al Hussein warned recently the country was at a "crossroads" between a fair vote and a route back to its "horrendously violent past".

Source: Agencies