NIAMEY -- A number of prisoners on Thursday escaped from a prison holding militants in west Niger's Tillabery region, according to the Ministry of the Interior.

The ministry did not specify in its statement how many prisoners managed to escape or how they escaped from the Koutoukale prison, which is located some 50 km northwest of the Nigerien capital Niamey and considered the safest in the country.

The prison detains many members of the Nigerian group Boko Haram and Sahelian militant groups.

Local authorities imposed an overnight curfew in the urban commune of Tillabery, located in the same region as the prison, but did not provide further details.