Opposition supporters demonstrated in Libreville

Riot police used tear gas to disperse hundreds of protesters as they tried to march through the capital, Libreville.

On Wednesday, the interior minister announced on national TV that President Bongo had won 79.2% of the vote.

His two main opposition rivals, Pierre Mamboundou and Zacharie Myboto, say they believe the results are not valid.

AFP news agency quotes a judicial sources as saying 23 people were arrested after Thursday's march.

A number of people were injured, the unnamed source added.

President Bongo, Africa's longest-serving leader, has ruled oil-rich Gabon in 1967.

He has now won three elections since a multi-party system was introduced in 1991.

The incumbent stood on his record of maintaining a stable Gabon in an unstable region.

But his opponents accuse him of using the nation's wealth to buy votes.