Many people have died after two assailants blew themselves up outside police headquarters and academy in the capital of Chad, whose forces have been on the frontline fighting Boko Haram militants, a police official says.

The twin attacks on Monday also left a number of people wounded, the source said on condition of anonymity.

Security in N'Djamena has been beefed up for months, after Chad sent its troops to fight the Takfiris who have been waging violence in northeastern Nigeria for six years.