An African student joins Islamic State

When Sadio Gassama decided to go into medicine, he started by giving free check-ups at his mosque in Senegal's poor southern region of Casamance. Now, the 25-year-old medical student says he is treating Islamic State fighters in Libya.

Until recently, many thought the peaceful, tolerant Sufi brotherhoods in countries such as Senegal could prevent more conservative and radical versions of Islam from taking hold in poorer parts of West Africa, like Mali and Niger.

But security experts say Gassama's story shows how the penetration of hardline Islamic Salafism, coupled with Gulf money and militant propaganda, is aiding recruitment, even from stable and democratic Senegal.

In particular, in their appeals to Africans, Islamic State propagandists are calling on doctors to make "hijrah", or pilgrimage, to their African stronghold of Sirte in Libya.

Pictures posted on Gassama's Facebook page before he joined Islamic State show him hugging his young niece. Now, he is brandishing a machine gun, his name stitched on to his military uniform.

Friends and family say Gassama's decision to join thousands of militants in Libya in December during the fifth year of his medical studies was sudden and unexpected.

His shocked father described him as a 'humanist' motivated by a desire to help others. A former professor called him a "brilliant student, incapable of hurting anyone".

But an interview with Gassama showed a darker side. Speaking from Sirte, he said he had been planning an attack in Dakar.