Six people including a policeman were killed in gun battles Wednesday in the latest violence in Burundi, as it awaits results from elections boycotted by the opposition and condemned internationally.

Clashes broke out in the capital's Cibitoke district, an opposition area that has been one of the heartlands of protests against President Pierre Nkurunziza's defiant bid for a third term.

Nearly 10,000 Burundians fled the country over the weekend before Burundi closed its borders ahead of controversial and violence-wracked elections in the troubled central African nation, the United Nations said Tuesday.

Since Burundi's political turmoil began in April, some 144,000 people have fled the country, with the numbers surging towards the end of last week, the U.N. refugee agency said.

Sitting in a quiet polling station in Burundi's capital Bujumbura, the four election officials have little better to do than listen to the radio.

Voters are shunning the ballot here in the key opposition Nyakabiga district, driven both by a fear of violence following weeks of unrest and a string of recent grenade attacks, as well as heeding a boycott call by the opposition.

Burundians voted Monday in controversial elections that were condemned internationally amid an opposition boycott and grenade attacks, with the election commission claiming an "enormous" turnout despite many stations being quiet.

Assailants threw grenades both in the capital Bujumbura and at some provincial voting centers ahead of Monday's parliamentary and local elections, the latest unrest in weeks of violence and a failed coup in which more than 70 people were killed, sparked by President Pierre Nkurunziza's defiant bid for a third term.

On the eve of highly-charged elections, U.N. Secretary-General Ban Ki-moon on Sunday urged the government of Burundi to ensure that voting takes place in a secure environment.

After months of turmoil, Ban had on Friday urged Burundi to delay the vote after the opposition announced a boycott, but the government rejected his appeal.

The African Union announced it would not act as an observer in Monday's parliamentary polls in Burundi, saying the conditions were not right for "credible elections" after weeks of violent protests and international calls for the vote to be delayed.

"Noting that the necessary conditions are not met for the organization of free, fair, transparent and credible elections... the AU Commission will not observe the local and parliamentary elections scheduled to take place this Monday," AU commission chair Nkosazana Dlamini-Zuma said in a statement on Sunday.

The head of Burundi's parliament on Sunday said he had left the nation due to the violence raging there and urged the president not to seek an "illegal" third term.

"For the moment, I am forced to stay in Brussels... I stayed here given the difficulties in my country, difficulties which are due to the illegal third mandate of the President of the Republic," Pie Ntavyohanyuma told France 24 news channel in an interview from Brussels.

Burundi's national electoral commission dismissed weeks of violence Sunday and said all was ready a day ahead of key polls in the central African nation that the U.N. warns should be postponed.

U.N. Secretary General Ban Ki-moon has called for the elections due Monday to be delayed after the opposition said they would not take part, as Burundi faces its worst crisis since its civil war ended nine years ago.

Burundi journalist union president Alexandre Niyungeko sits at a computer in a cafe in Rwanda. He should be busy covering his country's key parliamentary elections on Monday.

Yet, like scores of fellow journalists, as well as civil society activists and opposition politicians, he fled weeks of pre-election unrest to Kigali, capital of neighboring Rwanda.

Burundi's opposition parties announced plans Friday to boycott upcoming elections, saying it was not possible to hold a fair vote following weeks of violence over President Pierre Nkurunziza's bid to stay in power.

Civil society groups backed the move in a joint statement calling on voters to skip the "sham elections" and urging the international community "not to recognize the validity" of the polls.