Regional governors from Nigeria's 36 states headed into emergency talks Monday to discuss the country's power vacuum as calls grew for ailing President Umaru Yar'Adua to step down, officials said.

NONE "All the governors are meeting this evening to discuss matters of national importance, including the president's continued absence from the country," an official from a southern Nigerian state told AFP.

The meeting comes as Nobel laureate Wole Soyinka prepared to lead a march and rally in the capital Abuja on Tuesday, to protest Yar'Adua's seven-week absence from the country.

"We are displeased by the vacuum created by the long absence from office of President Umaru Yar'Adua," a spokesman for civil rights movement Save Nigeria Group (SNG), Yinka Odumakin, told AFP.

The growing speculation over Yar'Adua comes as Africa's most populous nation and second-largest oil exporter faces its most serious constitutional crisis in decades, with government business stalled amid opposition allegations of a cover-up over his condition.

International spotlight

The country has also been thrust into the international spotlight by Islamist fundamentalist violence in the north and the failed Christmas Day bombing of a US airliner by a young Nigerian, prompting its appearance on a 14-nation terror watchlist by the United States.

The 58-year-old president has not been seen or heard since he was flown to hospital in Saudi Arabia on November 23 for treatment for acute pericarditis, an inflammation of the membrane around the heart.

Aides have insisted he is responding well to treatment, but Nigeria's opposition has demanded proof that Yar'Adua is even alive.

"The speculations are false, the president is alive and actually getting better...he is very much conscious, can talk and has been talking," his spokesman Olusegun Adeniyi told AFP on Monday.

'Funny game'

Nigeria's main opposition party, Action Congress, Monday demanded immediate and tangible evidence of Yar'Adua's condition.

"In the absence of video evidence that the president is indeed getting well, it will become clear ... that there is a funny game going on somewhere," it said in a statement.

"Without concrete evidence...it will be safe to assume that the president has become so incapacitated that he can no longer write to the National Assembly," to empower the vice president to act on his behalf, as required by the constitution.

It said the country has been kept in the dark for too long and "one more day is too long, we want to know the truth today," the statement added.

A supplementary budget was rushed to his bedside for his signature last week, and the government was forced to strenuously deny opposition claims that the signature was forged. Some rights activists want the president declared missing.

Tuesday's rally will coincide with the first formal debate by lawmakers as both chambers of the National Assembly meet to debate the political vacuum created by the president's absence and lack of information about his condition.

"We will discuss the indisposition of the president," said Ita Enang, chairman of the House of Representatives' committee on rules and business.

Top politicians and human rights activists are among those listed to participate in Tuesday's street rally.

Soyinka, who won the 1986 Nobel Prize for Literature, is to address the rally, tagged "Enough is Enough", and protest at a slow down in government business and political reform since Yar'Adua was taken ill.

-AFP