Refuting speculations that he has been made to sign an undated resignation letter because of the deteriorating health of President Umaru Musa Yar'Adua, Nigerian vice-president on Sunday described the news as "false and mischievous."

"This story, we must add, is sheer mischief and dwells entirely in the imagination of its authors, their sponsors and co-travellers. This is wild and quite insulting claim that requires no further elaboration," Vice President Goodluck Jonathan said in a statement.

Nigerian president is undergoing treatment for acute pericarditis, a heart condition, in Saudi Arabia and there have been widespread rumours about him slipping into a coma or having died, a claim denied by his spokesman.

Though the constitution allows the vice-president to take over if the president is not able to govern or if he dies in office but an arrangement within the ruling Peoples Democratic Party (PDP) zones the presidential seat to the candidates from North while Jonathan is from South.

A newspaper here said that Jonathan has been made to sign an undated resignation letter which would be dated if the president dies or is found incapable of ruling the country.

Those behind the move want to ensure that the delicate power sharing arrangement between the North and the South is preserved, the newspaper said.

Yar'Adua, 58 is widely believed to have a history of kidney-related disease for which he has previously received treatment in both Germany and Saudi Arabia.