Ailing: Umaru Yar'Adua has not been seen in public since November
Senate may force Yar'Adua to step aside
The Nigerian Senate is set to debate a motion demanding that the country's ailing President Umaru Yar'Adua hand over power to his deputy in a bid to break months of political deadlock.
The debate, sparked after powerful state governors lobbied senators to pass the motion, is expected to be carried live on television.
Yar'Adua has been in a Saudi Arabian hospital since last November.
His absence has sparked legal challenges, Cabinet splits and mass protests.
The BBC said the Senate move is unprecedented - the Senate and state governors are usually loyal to the president, and the office of vice-president carries little weight.
Last week, a group of state governors - said to be increasingly concerned at the power vacuum emerging in Abuja - started lobbying for Vice-President Goodluck Jonathan to take control.
In theory, a motion could be approved by the Senate, the House of Representatives and Cabinet this week, allowing Jonathan to then be sworn in as acting president.
However, the legality of such a move is uncertain.
Meanwhile, the Senate is also expected to consider a move to impeach the president.
Two weeks ago, the assembly asked Yar'Adua to provide a letter confirming he was sick, to allow a formal transfer of power.
As yet, parliament has not received a letter.
It is understoof that anti-Yar'Adua factions are planning to insist on that the house receive a sick note by this Thursday if the president wants to avoid being impeached.
Last week a presidential aide told the BBC such a letter would be written "soon".
Yar'Adua has not been seen in public since flying to Saudi Arabia for medical treatment in November.
He gave a radio interview to the BBC's Hausa service in early January where he pledged to return to Nigeria as soon as the doctors would allow. he has made no statement since then.
Yar'Adua is suffering from an inflammation of the lining around the heart. He also has a history of kidney problems.