Presidential polls are taking place in Guinea-Bissau, four months after soldiers killed leader Joao Bernardo Vieira. Eleven candidates are contesting the election in the impoverished West African nation. Front-runners are Malam Bacai Sanha of the ruling party, and former presidents Henrique Rosa and Kumba Yala. President Vieira was killed in March in apparent revenge for the death of the head of the army in a bomb blast. He had ruled Guinea Bissau for a total of 23 years, from 1980-1999 and from 2005-2009. Drug trade About 600,000 of the country's 1.3 million residents are eligible to vote in the polls. A second round of polling could be held if there is no outright winner. Malam Bacai Sanha, who served as interim president from 1999-2000, is the ruling party candidate. He faces his biggest challenges from opposition leader and former President Kumba Yala, who was overthrown in a 2003 coup, and from Henrique Rosa, who served as interim president from 2003-2005. All three leading candidates have promised to bring peace and stability to the nation. They have also promised to tackle the drug trade in Guinea-Bissau, which has become a transit point for gangs shipping cocaine from South America to Europe. Source: BBC