President Umaru Yar'Adua refuses to say exactly what he suffers from
Nigerian President Umaru Yar'Adua has appeared in public for the first time in two weeks, marked by speculation and rumour about his health.
He presided over the swearing-in of new military chiefs in the capital Abuja.
The president, who suffers from a chronic condition which affects his kidneys, was receiving treatment in Saudi Arabia.
President Yar'Adua also sacked a high-ranking government official who had been linked with the rumours.
Secretary to the Government of the Federation Baba Gana Kingibe was removed and replaced by former Defence Minister Mahmud Yayale Ahmed, it was announced by e-mail.
The president's continued ill-health posed a problem for Nigeria's constitution, political scientists told the BBC.
If he were to step down, or die, he must be replaced by Vice-President Goodluck Jonathan, who is from the country's southern Delta region.
But according to the ruling People's Democratic Party's own formula for sharing power among the country's regions, the president must be a northerner.
Rumours circulating among journalists and political pundits said the president was going to step down because of his ill-health and Mr Kingibe would step in as a kind of "puppet-master" Vice-President.
Mr Kingibe, from Borno state in north-west Nigeria, was the vice-presidential running mate in the 1993 elections, annulled by former military ruler Ibrahim Babangida.
He was also Minister for the Interior under Mr Babangida's successor General Sani Abacha.
It was during this time that Shehu Yar'Adua, the current president's brother, was imprisoned.
Shehu Yar'Adua, a former vice-president, died in jail.
When he left Nigeria, President Yar'Adua said he was going to Saudi Arabia to visit the Muslim holy city of Mecca.
Rumours about his worsening state of health spread after it was confirmed he was in a hospital in Jeddah.
Spokesman for the opposition Action Congress (AC) Lai Mohammed told the BBC's News website the country was on "auto-pilot".
President Yar'Adua has suffered from a condition affecting his kidneys for at least 10 years.
He has twice been flown to Germany for emergency medical treatment in the last 18 months.
Mr Yar'Adua has refused to say exactly what condition he suffers from, and has repeatedly said in interviews that his life is "in the hands of God."