A regional bloc of West African countries has recognised Umaro Sissoco Embalo as the winner of Guinea-Bissau's presidential election, after months of dispute over the results.

The country's electoral authority has repeatedly said Embalo, a former army general and prime minister, won a runoff presidential vote on December 29.

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But losing candidate Domingos Simoes Pereira, from the long-ruling PAIGC party, called the election fraudulent and took the case to the Supreme Court, which has not yet ruled.

On Thursday, the Economic Community of West African States (ECOWAS) bloc said in a statement that they recognised Embalo as president but also called for constitutional reform to be put to a referendum within six months.

Embalo had declared himself president in February without waiting for the court, creating a political impasse. At the time, ECOWAS said his inauguration had taken place "outside legal and constitutional frameworks".

In its statement on Thursday, the regional bloc noted the standoff had not yet been resolved and provided no explanation for why it now saw Embalo's presidency as legitimate.

"In the face of the persistence of this blockage and after an in-depth analysis of the country's political situation, the ECOWAS heads of state and government decided to recognise the victory of Mr. Umaro Sissoco Emablo," the statement said.

The post-election controversy dashed hopes that the vote would end years of institutional chaos. Former President Jose Mario Vaz, who was eliminated in the first round of voting last November, cycled through seven prime ministers in five years amid a dispute with Pereira's party, which controls the most seats in parliament.

Pereira has accused Embalo of illegally seizing power with the backing of the country's military, which has been involved in nine coups or attempted coups since independence from Portugal in 1974.

The Supreme Court has said it cannot rule on Pereira's challenge in the absence of its chief judge, who fled the country for Portugal after the election, saying he feared for his safety.