ABUJA, Nigeria - Nigeria's Acting President Goodluck Jonathan was sworn in as head of state on Thursday following the death of President Umaru Yar'Adua and will lead the country to its most fiercely contested polls since its return to democracy.

Jonathan took the oath of office in front of government ministers, state governors and ambassadors at the presidential villa in Abuja almost 12 hours after Yar'Adua died, aged 58, following a long battle with kidney and heart ailments.

Jonathan had already been running Africa's most populous nation as acting president for several months while Yar'Adua was incapacitated.