Nigeria's president, Umaru Yar'adua, has died after a long illness, an official at his office has said.

He reportedly died on Wednesday evening at the Aso Rock presidential villa in the Nigerian capital, Abuja.

However the country's information minister says she has not yet verified the report.

Yar'adua returned to Nigeria in February after receiving medical treatment in Saudi Arabia, but had not been seen in public since.

He had been suffering from an inflammation of the lining around the heart and was known also to have problems with his kidneys.

During his absence he failed to formally transfer his powers to his vice president, Goodluck Jonathan, sparking a constitutional crisis in Nigeria, Africa's most populous nation with 150 million people.

Jonathan assumed the presidency on February 9 after a vote by the National Assembly while Yar'adua was still in Saudi Arabia.

However, the assembly left open the possibility for Yar'adua to regain power if he returned to the country in good health.

Yar'Adua took office in 2007 in a country notorious for corruption and was praised by many for being the first leader to publicly declare his personal assets when taking office - setting up a benchmark for comparison later to see if he misappropriated funds.