Harare (AFP) - Zimbabwe's 93-year-old President Robert Mugabe, declaring "I am not dying," sought Saturday to brush aside growing concerns about his health after his wife urged him to name a successor.

Mugabe's medical trips to Singapore have become frequent in recent years, fuelling questions about his health. His last visit was early this month for what was described as a "routine medical check-up".

"There is the issue that the president is going. I am not going. That the president is dying. I am not dying," Mugabe told thousands of supporters at a rally in his home town of Chinhoyi.

His remarks came after his wife Grace urged him to name a successor in a bid to end the factionalism threatening to tear apart his ruling ZANU-PF party.

"I thank God for having lived to this day. I thank God for the good life. I have an ailment here and there (but) my organs… my heart and liver are very firm. Recently, doctors were actually surprised by the strength of my bones," Mugabe said.

He said he had followed a strict exercise routine from the years he was imprisoned during the fight against colonial rule in the 1970s.

Mugabe, who spoke for more than an hour at the rally, now walks with difficulty and sometimes dozes off during meetings.

In 2011 and 2014 he had eye surgery in a hospital in Singapore.

His health has been the subject of increased speculation and authorities in March arrested two journalists over a report alleging that he was "in bad shape".

In 2016, the government had to deny that he had died abroad during his annual vacation.

Mugabe has declined to name a successor and his party has been riven by divisions for years.

On his succession, Africa's oldest leader said: "I want to see whether the situation is ripe."

"Are those who are my subordinates united? I see some are divided tribally. Some denigrate each other."

Despite Mugabe's age, the party last year endorsed him as its candidate for the 2018 general elections.

On Thursday, Mugabe's wife Grace called for an end to uncertainty over his successor.

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"President, don't be afraid. Tell us who is your choice, which horse we should back," she told a meeting of the women's league of the ZANU-PF.

"If you tell us the horse to back, we will rise in our numbers and openly support that horse. Why should our horse be concealed?"

The succession race is seen as between Vice President Emmerson Mnangagwa and a group called "Generation 40" or "G40" because its members are generally younger, which reportedly has Grace's backing.