(Adds background on force, date of transfer of authority to AU)
ADDIS ABABA, Dec 13 (Reuters) - The African Union has authorised increasing an African force being deployed to Central African Republic to 6,000 troops from 2,500, a senior AU official told Reuters on Friday.
The United States began airlifting Burundian troops to Central African Republic this week as part of efforts to help African and French forces prevent a descent into civil war.
The Burundians are due to join an African peacekeeping force that has struggled to contain violence in the country that has killed more than 500 people in the past week.
Former colonial power France has also boosted its troop contingent, two of whom were killed this week.
"The decision by the Peace and Security Council (PSC) is to authorise us to increase the force. We can go up to 6,000, depending on the needs," El Ghassim Wane, Director of the African Union's Peace and Security Department, said.
"Within three months the PSC will meet again to review the strength based on the evolution of the situation and our assessment of the situation on what needs to be done," he said.
Previously a Central African force, the mission is being broadened to fall under African Union command. The decision to increase the force numbers followed meetings between African leaders in France last week.
The existing force deployed by the Economic Community of Central African States will become an African Union mission to be known as MISCA. Wane said the formal transfer of authority takes place on Dec. 19.
(Reporting by Aaron Maasho; Writing by Edmund Blair; Editing by John Stonestreet)