A confidential UN report links the development of homemade explosives by the Islamist extremists to an increase in bombings in the Somali capital, Mogadishu.

The claim is based on analysis by a panel of experts of samples taken following 20 attacks.

The UN has not commented on the report.

Since September, there have been at least 19 car- or truck-bomb attacks by al-Shabab in which five people or more have died.