Nigerian President Umaru Yar'Adua has died at his presidential villa following a long illness. The government announced seven days of national mourning and said the president would be buried on Thursday. Vice-President Goodluck Jonathan has been sworn in as head of state in a ceremony in the capital Abuja. Mr Yar'Adua, 58, came to power in 2007 promising many reforms. Analysts say he made the most progress in tackling unrest in the oil-rich Niger Delta.