The losing candidate in Guinea Bissau's presidential run-off poll has filed a Supreme Court challenge against the election result.

Domingos Simoes Pereira said there had been substantial fraud, with votes cast surpassing the number of voters in some areas.

However, African Union observers said the poll was free and fair.

The former Prime Minister and Army General Umaro Cissoko Embalo, who won 54% of the vote, has insisted that he was the rightful winner.

Mr Embalo has presented himself as a unifier of a politically divided country, which has had seven prime ministers in the past five years.