"The Senate urged the president , to formally notify the National Assembly of his medical vacation pursuant to section 145 of the 1999 constitution," Senate President David Mark said, following two days of closed-door debate by lawmakers.

Article 145 states that whenever the president submits a written declaration that he is going on vacation or otherwise unable to perform his duties, the vice president takes over as acting president until he writes again to the contrary.

Although the Senate does not have the authority to force Yar'Adua to hand over power, parliament could in theory move to impeach him for misconduct if he fails to heed its call.

The Senate's decision after what lawmakers described as hours of "painstaking" debate is another blow to the efforts of Yar'Adua's "kitchen cabinet" to keep him in power.

http://af.reuters.com/article/topNews/idAFJOE60Q0BV20100127?pageNumber=2&virtualBrandChannel=0