The Supreme Court in Senegal has rejected the final appeal by the imprisoned former mayor of Dakar, Khalifa Sall, against a corruption sentence - one day before presidential election campaigning is due to start.

Mr Sall, who is one of the main opposition challengers, was sentenced last March to five years in prison, accused of embezzling $3m (£2.4m).

The opposition has accused President Macky Sall of sidelining opposition figures by selectively enforcing corruption laws. He is standing for re-election in February.

Another challenger has been exiled to Qatar. Karim Wade, who is the son of the former President Abdoulaye Wade, was banished after being given a conditional pardon for corruption, and reportedly told not to return to Senegal until after the election is over.