Guinea-Bissau has declared a week of national mourning after President Joao Bernando “Nino” Vieira was killed in an apparent revenge attack.The head of the West African state was shot dead by a group of rebel soldiers on Monday morning as he tried to flee his house in the capital, Bissau. Officials say it was in retaliation for the death in a bomb blast of the head of the armed forces, Batista Tagme Na Wai, with whom he had been locked in a power struggle. At least six other people were killed by the explosion. Na Wai is from the biggest Balante ethnic group, which dominates much of military life. Vieira was from the smaller Pepel tribe. Small arms and heavy weapon fire resounded in the capital for hours afterwards the bombing of the army barracks. As a result the streets were largely deserted this morning as it was unclear who was in control of a nation that has become a key transit point for drug smuggling. Amid fears the conflict would spiral out of control, the armed forces spokesman issued assurances that the situation in the country is calm. But he failed to say whether the President’s killers had been apprehended. Political leaders have also been meeting army chiefs to discuss maintaining the country’s democratic institutions. The former Portuguese colony, one of the world’s poorest states, has a history of military take-overs. Last November the presidential palace came under attack in a failed coup attempt.