Pope Francis has prayed for victims of violent protests in the west African nation of Gabon, calling attention to what he described as a "grave political crisis" in the former French colony.

In remarks to the faithful in St Peter's Square on Sunday, Francis also encouraged the Gabonese people, particularly Catholics, to be "builders of peace while respecting legality, dialogue and brotherhood."

Gabon was marked by violent protests after the results of an August 27 presidential election were announced. The opposition candidate mounted a legal challenge, accusing the incumbent leader of fraud.