Security forces launched an assault in the early hours of Saturday on a Burkina Faso hotel to rescue hostages held by Al-Qaeda-linked gunmen, the French ambassador to Ouagadougou Gilles Thibault said on Twitter.

"The assault has started, the various components of the armed forces and security forces have begun their missions," Thibault said. 

At least 20 people have been killed so far in the bloody siege on a hotel popular with United Nations staff and foreigners.