HARARE (AFP) - Zimbabwean President Robert Mugabe, who celebrated his 93rd birthday last week, flew to Singapore on Wednesday (March 1) for a "scheduled medical review", his spokesman said.

Mugabe appeared frail at his birthday party on Saturday, when he stood for more than an hour to deliver his speech, but he paused for lengthy periods and mumbled at times.

"The President left this morning for Singapore for a scheduled medical review," his press secretary George Charamba told the state-run Herald newspaper. "We expect him back in the country early next week."

Mugabe, the world's oldest national leader, has held power since 1980 during a reign marked by repression of dissent, vote-rigging and a sharp economic decline for the country.

He recently spent several weeks in Asia on his annual vacation, returning in late January, though it has not been officially confirmed that he had medical treatment during the trip.

He has made regular trips to Singapore for medical check-ups, and his health is a frequent subject of speculation.

In 2011, WikiLeaks released a US diplomatic cable from 2008 saying that Mugabe was reported to have prostate cancer and had less than five years to live.

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

The ruling Zanu-PF party has been riven by factionalism for years as Mugabe has declined to name a successor.

Senior Vice-President Emmerson Mnangagwa is seen as a leading contender to be the next president, as is Mugabe's 51-year-old wife, Grace.

Mugabe's spokesman was not available to comment to AFP.