Guinea-Bissau's parliament rejected a bill on Tuesday that would have granted amnesty to the leaders of the latest of a long line of military coups last year, according to an AFP journalist in the chamber.

The motion put forward by the transitional government needed a majority among the country's 100 lawmakers but just 40 gave it the go-ahead, with a quarter of lawmakers absent, according to acting speaker Braima Sori Djalo.

"That's democracy. Every member voted according to his conscience," he said.

Guinea-Bissau, a nation of just 1.6 million people, has suffered chronic instability since independence from Portugal in 1974.

The volatility has fanned poverty, attracting South American drug cartels which have turned it into a hub of cocaine trafficking for west Africa.

Former army chief Antonio Indjai overthrew the regime of former premier Carlos Gomes Junior on April 12 last year before agreeing to hand power to a civilian transitional government.

The caretaker regime headed by President Manuel Serifo Nhamadjo is due to hold presidential and parliamentary elections on November 24.

The national assembly did not reveal the details of the bill but legislators interviewed by AFP said it would have handed immunity from prosecution to civilians and military personnel implicated in the coup.