Umaru Yar’Adua, Nigeria’s president, has sought to strengthen his grip on power by shaking up government ministries after a health scare triggered frantic speculation over whether he was too sick to survive in office.

Rumours that Mr Yar’Adua had died swirled around Abuja, the capital, last week when he failed to return from Saudi Arabia after having medical treatment, triggering fears of a leadership crisis in Africa’s biggest oil exporter.