The EU mission regrets the absence of a multi-party contest in the Burundi election

European Union observers expressed regret on Wednesday that Burundi's incumbent President Pierre Nkurunziza had contested elections unchallenged, after all six opposition candidates boycotted Monday's vote.

Renate Weber, who heads the European Union mission, praised Burundi for holding a peaceful presidential election but criticised the government for limits on political expression.

Nkurunziza was re-elected for another five year-term with 91.62 percent of the vote, the national electoral commission (CENI) said, but top opposition contender Agathon Rwasa went into hiding before the election.

"The EU mission saluted the calm that characterised the June 28 election, but regretted the absence of a multi-party contest in the election," said Weber.

"This is grounded on the withdrawal of six candidates from the competition, distrust of the opposition in the national electoral commission (and) limitations of meeting and political expression by the government," she told reporters.

CENI said turnout was 76.9 percent, lower than the 91.7 percent recorded during district polls on May 24. Opposition parties say the turnout was between 30 and 40 percent.

The boycott followed complaints of fraud in district elections in May. Opposition parties had sought a re-run of the vote, which Nkurunziza's party won, but CENI rejected the demand.

A spokesman for 13 opposition parties said the presidential election had contravened the constitution and they would not recognise Nkurunziza as president.

"The constitution is clear; it states that Burundi is a multi-party democracy. But in the present case, we just have one candidate for one political party. For us, Nkurunziza is not a legal president," spokesperson Leonard Nyangoma told Reuters.

Rwasa, a former rebel leader, said he went into hiding after learning that the government wanted to arrest him on charges that he planned to mount a new insurgency.

In a tape recording received by Reuters on Wednesday, Rwasa said he had also been threatened for rejecting last month's district polls, which were seen as a test of stability for the coffee-producing country of eight million.

By Patrick Nduwimana for Reuters