Six people have been killed in a gunbattle in the troubled nation of Guinea-Bissau in what officials are calling a failed coup attempt.

Officials in the West African country say government troops repelled an attack before dawn on Sunday on an air force base near the capital, Bissau.

Casualties among the government forces could not be confirmed. Witnesses say authorities tightened security in the capital after a two-hour gunbattle and that the situation is calm.

Guinea-Bissau has suffered chronic unrest since independence from Portugal in 1974, with frequent coups and counter-coups. A military government seized power in April, interrupting a presidential election between the first and second rounds.

The coup leaders later installed a transitional government to organize new elections, winning the support of West African regional bloc, ECOWAS. But the transitional government has not secured wider international recognition, with critics saying it remains under army influence.

The instability has made Guinea-Bissau a hub for international cocaine traffickers.