The outcome of Guinea-Bissau's presidential election was thrown into doubt on Friday after the Supreme Court called for a clarification of the tally hours after the electoral commission released the final results.

Former prime minister and ex-army general Umaro Cissoko Embalo has been hailed as the winner of last month's runoff vote. But runner-up and ruling party candidate Domingos Simoes Pereira has contested the results saying the election was marred by fraud.

In a ruling backed by five out of eight judges, the Supreme Court called on the national electoral commission to clarify tabulation procedures used for the vote "to ensure the freedom and fairness of the exercise in electoral will".

The commission did not immediately respond to the court's decision. Earlier on Friday it released the final results, confirming Embalo's victory with 54% of votes cast versus Pereira's 46%.

Uncertainty over the outcome of the election would extend protracted political turmoil in the coup-prone West African country of 1.6 million people that has hobbled economic development and made voters weary of the ruling class.

A representative of Embalo's MADEM-15 party rejected the court's ruling saying the publication of the final results made his victory irreversible.