Guinea-Bissau's electoral commission says it will release provisional presidential election results Wednesday, a day after five candidates called for the results to be annulled because of alleged fraud.

Unofficial early results from Sunday's poll give the lead to former prime minister Carlos Gomes Junior of the ruling African Party for the Independence of Guinea and Cape Verde .

Trailing in second place is former president Kumba Yala, the leader of the main opposition party, who was ousted from office in a bloody military coup in 2003.

Mr. Yala is among the five candidates who say the election lacks credibility because it was rife with fraud and irregularities.

International election observers say the poll appears to have been free and fair.

The fraud claims have raised fears that trouble is looming in the coup-prone country, where former military intelligence chief Samba Diallo was killed hours after the polls closed.

The winner will replace the late president Malam Bacai Sanha who died in January after a long illness.

While Mr. Sanha was hospitalized in December, a struggle within the military and an apparent coup attempt took place.

Since winning independence from Portugal in 1974, Guinea Bissau has struggled through a dictatorship, three coups and the 2009 assassination of a president.

The country has also become a transit point for cocaine smugglers.