Africa's oldest leader and world's second oldest after Shimon Peres of Israel, Mugabe has ruled Zimbabwe since independence from Britain in 1980.

Despite speculation over his physical fitness Mugabe accepted nomination from his ZANU-PF party to stand for another five-year term in elections due in July.

But doubts have been cast on whether he still has the physical and mental stamina to go through an election campaign and complete another full term.

"Mugabe's age and health will not allow him to remain active," said Blessing Vava, a Harare-based independent political commentator.

"Look at Pope Benedict XVI who recently announced his retirement at 85, saying his body and health does not allow him to carry duties that he used to do."

Observers think Mugabe wants to cling onto power for as long as is possible, then pick a successor of choice who will ensure he is shielded from prosecution for any rights abuses he may face.

"He is looking for a safe exit from politics by remaining in power until death or handing over to a successor who will guarantee that he will not be prosecuted for rights violations," said Charles Mangongera, another independent analyst.

He added "Mugabe realises that this is a do or die situation" and "for him I think it is an issue of personal interest rather than national interest."

But the longtime leader, who is blamed for having driven the country to pariah status, is likely to have a tough time working through an election campaign.

"Mugabe is an old man, he is not going to be moving around (the country) like he used to," said Vava. Mangongera said Mugabe faces an election hurdle in contesting with a much younger candidate, arch-rival Prime Minister Morgan Tsvangirai, who is nearly 30 years his junior.

"I don't see Mugabe withstanding a gruelling election campaign," Mangongera said.

"Look he is 89. I have seen ...television footage of him struggling to scale steps.

That is indication that he is frail. Age will not allow Mugabe to mount a credible election campaign."

Mangongera said Mugabe's calls for peace ahead of the referendum on the draft constitution next month and elections are signs that he wants to redeem himself from past wrongs that have tainted his international image.

"If you listen to his language in the past months, he has been conciliatory, speaking like a statesmen. It is an attempt to secure his legacy," he said.

Mugabe and Tsvangirai were forced into a power-sharing government to avoid a tip into full scale conflict in the aftermath of a bloody presidential run-off election in 2008.

Mugabe is expected to offer his black empowerment drive to take over majority stakes in foreign owned companies as the main campaign tool.

A victory for the 89-year-old Mugabe would extend his 32 years in power, a reign that in the last decade has been marked by economic meltdown and serious rights violations.