Polling stations have opened in Burundis controversial presidential elections with Pierre Nkurunziza widely expected to win a third consecutive term. Shortly before voting started on Tuesday, at least two people - a policeman and a civilian - were killed, according to witnesses, in a string of explosions and gunfire in the capital Bujumbura, the epicentre of three months of anti-government protests. On Tuesday, Al Jazeeras Haru Mutasa, reporting from Bujumbura, said that one of the opposition members was also killed overnight in the citys Nyakabiga neighbourhood. The incident prompted a big crowd to gather there in protest in the morning. About 3.8 million Burundians are eligible to vote in the polls, which the opposition and civil society groups are boycotting, claiming they will not be free and fair. The opposition have denounced the candidacy of the incumbent president as unconstitutional and a violation of the 2006 peace deal that ended a dozen years of civil war and ethnic massacres in 2006. The nations constitutional court has ruled in the presidents favour, however, maintaining he is eligible for a third term because he was chosen by legislators - and not popularly elected - for his first term. Despite a facade of pluralism, this is an election with only one candidate, where Burundians already know the outcome, said Thierry Vircoulon, from the International Crisis Group, a think-tank that has warned the situation has all the ingredients to kick-start a renewed civil war. Ban Ki-moon, the UN secretary-general, has called on authorities to do all in their power to ensure security and a peaceful atmosphere during the election. He [Ban] further calls on all parties to refrain from any acts of violence that could compromise the stability of Burundi and the region, his spokesman said in a statement on his behalf. More than two months of anti-Nkurunziza protests, which have often been violently repressed, have left at least 100 dead since late April. Independent media has been shut down and many opponents have fled - joining an exodus of more than 150,000 Burundians who fear their country may again be engulfed by widespread violence. Doctors Without Borders (MSF) said on Monday about a thousand people were fleeing each day into Tanzania, crossing the border through the forest ... many travelling in the dark on foot and without belongings. In mid-May, rebel generals attempted to overthrow Nkurunziza in a coup. After that failed, they launched a rebellion in the north of the country. Last-ditch crisis talks mediated by Uganda broke down on Sunday. The government has opted to isolate itself and go ahead with pseudo-elections, said Leonce Ngendakumana, a prominent opposition figure, after talks collapsed. They have refused to save Burundi from sliding into an abyss, said Jean Minani, another opposition figure. A poor and landlocked former Belgian colony, Burundi is situated in the heart of central Africas troubled Great Lakes region. Analysts say renewed conflict in the country could reignite ethnic Hutu-Tutsi violence and bring another humanitarian disaster on the region. The conflict also risks drawing in neighbouring states - much like in the war-torn east of the Democratic Republic of Congo. The last civil war in Burundi left at least 300,000 dead. Al Jazeera