Yar'Adua has been at the King Fahd Armed Forces Hospital in the Red Sea city of Jeddah, the administrative official told AFP without specifying his medical condition or the treatment he is undergoing.

Saudi military police were seen guarding the hospital, which is run by the Saudi defence ministry and where ruling family members and senior officials are usually treated.

Two Nigerian independent dailies said on Saturday that Yar'Adua, 57, is believed to have undergone surgery in Saudi Arabia.

Nigerian authorities have denied the president is out of the country to seek medical attention, saying he is on a religious pilgrimage.

Yar'Adua left Nigeria around 10 days ago for the Muslim lesser hajj, or umrah, which is performed in Mecca in Saudi Arabia, according to the government.

Nigeria's government on Sunday again sought to dispel speculation over the president's health, saying he is well and fit to run Africa's most populous nation.

"The federal government wishes to restate here that Mr President is very well and healthy," said Information Minister John Odey.

"He is in good health to steer the affairs of the state to bring about better livelihood for the generality of the people of Nigeria," Odey said in a statement to the media.

Odey said the head of state is expected back in Nigeria "soon after his trip to Saudi Arabia where he has gone on lesser hajj".

The Action Congress (AC), one of Nigeria's leading opposition parties, meanwhile criticised the government "for feeding the public with deliberate lies" on the president's health.

"What should have earned the president the sympathy and prayers of his countrymen and women has again become a matter for wild speculations," AC spokesman Lai Mohammed said in a statement.