Abdullahi Yusuf ended an ignominious four years as Somalia’s president by resigning on Monday, giving fragmented Islamist groups in the war-ravaged country a chance to exert new influence over its future.

Mr Yusuf, a former warlord, was elected as the head of a western-backed interim government in 2004, the latest in more than a dozen attempts to form an effective central administration since the last one collapsed in 1991.