Voters went to the polls in Guinea-Bissau Sunday for a presidential runoff between two former heads of state of the coup-prone West African nation, whose veteran leader was assassinated in March. However, amid fears of violence when results are known, the country's army chief, General Zamora Induta, said candidates should turn to the courts if there are any disputes, warning on public radio that the military 'will not allow any threat to public order, stability and internal peace.' The election was triggered by the killing of long-time president Joao Bernardo Vieira by soldiers on March 2, in an apparent revenge attack after the assassination of then army chief General Batista Tagme Na Waie in a bombing. The runoff is between ex-presidents Kumba Yala and Malam Bacai Sanha, who won the biggest share of the vote in the first round on June 28. Sanha secured 39.59 percent of the first-round ballots -- a 10-point advantage over Yala. The African Union's special envoy Joao Miranda said he had met with both men and appealed for 'calm and a spirit of fair play.' Miranda said: 'They told me the loser would congratulate the winner and would promise to work with him to guarantee peace and stability.' Observers hope the new president will bring a degree of stability to the former Portuguese colony of 1.3 million people, which has suffered repeated coups since independence in 1974 and now is a haven for cocaine distributors. 'This election is very important because it will lead to the normalisation of the country,' interim president Raimundo Pereira told reporters after he voted in his constituency on the outskirts of the capital Bissau. 'It's an important step so that we can work, to have legitimate organs of state. I hope that that will put an end to the violence' which has destabilised the country for more that a decade, he added. The national electoral commission (CNE) said about 150 international observers would be on the ground for Sunday's vote and nearly 4,900 soldiers, police and paramilitary would be deployed to ensure security. At mid-day CNE spokesman Orlando Viegas said the voting was taking place without any reported incidents. In central Bissau, Sidi Mankale, the electoral official in charge of one polling station in a former football club, said: 'We began at 7:00 am (0700 GMT) and its about the same turnout as the first round.' In the Chao Pepel district of Bissau, voters were thin on the ground, but electoral official Ankouan Lopez said: 'There aren't many voters because people are going to church first before coming to vote.' Guinea-Bissau has been overwhelmed by the international drugs trade, becoming a key transit point in cocaine smuggling between South America and Europe. But another priority for the new president will simply be clinging on to power. None of the three presidents elected in the past 15 years has managed to complete his full five-year term. The murder of Vieira, who ruled Guinea-Bissau for much of the past 25 years, came about a decade after the military ousted him during a previous stint as president. In June, the army killed two senior political figures in what they claimed was an operation to foil a coup plot. Sanha, 62, the candidate for the ruling African Party for the Independence of Guinea and Cape Verde (PAIGC), served as interim president from June 1999 to May 2000. Yala, 56, who is running Sunday as head of the Social Renewal Party, was forced out by the army in 2003. Yala and Sanha have already faced each other in a second-round runoff for Guinea-Bissau's presidency in 2000, when Yala emerged victorious. Both rounds of the election have been financed entirely by the international community at a cost of 5.1 million euros (7.2 million dollars). Polls are set to close at 5:00 pm and preliminary results are expected to be announced in the next few days. 