Mugabe, right, formed a power-sharing government with his rival, Tsvangirai, at left, in 2009 [Reuters]

Robert Mugabe, Zimbabwe's president and Africa's oldest leader, has celebrated his 88th birthday, denying reports he has cancer.

Mugabe declared himself "fit as a fiddle" on Tuesday, scoffing at calls to retire and pushing for new elections this year.

"The day will come when I will become sick," Mugabe said in an interview on state-owned Radio Zimbabwe, dismissing fears about his health.

Making light of numerous media reports of his sickness, Mugabe, a Roman Catholic, said: "I have died many times - that's where I have beaten Christ. Christ died once and resurrected once."

Presidential officials said he would celebrate his birthday at a family dinner at his home in the capital Harare, with a  celebration rally taking place in eastern Zimbabwe on Saturday.

Power-sharing deal

Mugabe, in power since independence from Britain in 1980, said he will stand again in new elections that he insisted should be held this year - with or without the new constitution required under Zimbabwe's power-sharing deal with Morgan Tsvangirai, the prime minister.

"I came from the people and the people, in their wisdom, our members of the  party, will certainly select someone once I say I am now retiring, but not yet," Mugabe said.

Mugabe was chosen in December by his ZANU-PF party to stand again as its presidential candidate.

"There is no one who can stand and win at the moment," he said of the contenders in his party jostling to succeed him.

"We just must have elections. They just must take place with or without a new constitution. If others don't want to have an election then they are free  not to participate."

Cancer claims

Mugabe's health has been the subject of much speculation, especially since WikiLeaks, the whistleblower site, released last year a 2008 US diplomatic cable saying that Zimbabwe's central bank chief, Gideon Gono, had told then-US ambassador, James McGee, that Mugabe had prostate cancer and had been advised by doctors he had less than five years to live.

Mugabe's health has been cited as one reason that a faction of his ZANU-PF party has pushed to rush new elections.

Mugabe formed a power-sharing government with Tsvangirai in 2009 to repair an inflation-ravaged economy and avoid a political meltdown after a bloody presidential runoff election.

The two rivals agreed to a number of reforms including amending electoral and media laws and drafting a new constitution to pave the way to fresh polls.

But work on the new charter has progressed in fits and starts, hindered by attacks on public outreach meetings by supporters of Mugabe's ZANU-PF party. Mugabe has repeatedly pressed for elections this year, but Tsvangirai wants a new constitution to be in place before the election.