ABUJA - President Umaru Yar'Adua arrived back in Nigeria yesterday after three months in a Saudi Arabian hospital, renewing uncertainty over the leadership of the country.

Hours later acting president Goodluck Jonathan postponed a weekly cabinet meeting, summoning ministers instead to a special briefing.

"The acting president has directed me to announce that this meeting is hereby postponed. A special meeting is scheduled to be held by 2pm," Mahmud Yayale Ahmed, secretary to the federal government, told ministers waiting in the presidency.

There was no immediate word on Yar'Adua's condition but a presidential adviser said it was unlikely he would immediately resume office, suggesting Jonathan would remain acting head of state for now.

Yar'Adua's absence brought sub-Saharan Africa's second biggest economy to the brink of constitutional crisis and threatened to paralyse the business of government, until Jonathan was sworn in as acting leader two weeks ago.

Jonathan has since adopted the mantle of leadership, reshuffling ministers, pledging to tackle chronic power shortages and forge ahead with an amnesty for rebels in the oil-producing Niger Delta.

"The news of the president's arrival is reportedly causing a lot of anxiety in Abuja especially among politicians, many of whom had prepared themselves for a post-Yar'Adua era," Nigerian newspaper NEXT said on its website.

A senate resolution passed on February 9 stated that Jonathan would cease to be acting president once Yar'Adua stated in writing to the leaders of both houses of parliament that he had returned from "medical vacation".

But Nigeria's politicians have been flexible in their reading of the constitution during the crisis.

"The senate resolution was very clear. It says the acting presidency lapses once the president sets foot in Nigeria," one of Yar'Adua's close allies said. - Reuters