Burundi's president has been declared as a candidate for a controversial third term in office, his ruling party announced, despite mounting protests over the move that the opposition says is unconstitutional.

There was tight security as the ruling CNDD-FDD party opened a special congress on Saturday morning, during which Pierre Nkurunziza was officially designated as the party's candidate.

"We wish to announce to the national and international community that the member who has been selected to represent us in the elections is Pierre Nkurunziza," the head of CNDD-FDD, Pascal Nyabenda, announced after a party meeting.

He said Nkurunziza, a former rebel leader who has already served two-terms as president, "has the right to be elected".

Delegates underwent thorough searches before being allowed into the venue. Police and soldiers have also been deployed on the streets of Bujumbura since Friday evening.

No Western ambassadors were present at the congress - a sign of unease among key donors over Nkurunziza's bid to stay put. Only the Russian ambassador and several regional diplomats were present.

Fears over violence

There are fears that the political crisis, during which President Pierre Nkurunziza's ruling CNDD-FDD party has also been accused of intimidating opponents, could push Burundi back into violence.

The country, situated in Africa's troubled Great Lakes region, only emerged from civil war in 2006.

The opposition has vowed to take to the streets to challenge Nkurunziza's candidacy for the June 26 presidential elections. They argue his refusal to step aside violates the constitution as well as the peace deal that ended the civil war.

An AFP reporter said many residents could be seen doing last-minute shopping in an apparent bid to stockpile supplies just in case unrest breaks out.

In addition to banning all demonstrations, the government has also threatened to call out the army.

The influential Catholic Church has also spoken out against the president's plans to stay put, and earlier this month UN rights chief Zeid Ra'ad Al Hussein warned that the country was at a "crossroad" between a fair vote and a route back to its "horrendously violent past".

Refugee crisis

Thousands of Burundians have fled the country in recent weeks to neighbouring Rwanda and Democratic Republic of Congo, according to the UN's refugee agency, which has also warned that the numbers of refugees could swell "with more political tension rising and more acts of violence being reported".

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

Many residents of Bujumbura also left the city for the weekend, amid fears of violent clashes.
Burundi's constitution only allows a president to be elected twice - for a total of 10 years in power - but Nkurunziza argues he has only been directly elected by the people once.

For his first term, beginning in 2005, he was selected by parliament. The opposition boycotted the last elections in 2010, alleging fraud.

Source: Agencies