Zimbabwe's President Robert Mugabe is in Singapore for medical reasons, prompting opposition figures to question whether the 93-year-old still has the stamina to run the country.

State media, quoting an information ministry statement, says the world's oldest head of state left Friday for a "routine" medical checkup and will be back in Zimbabwe later this week. This is Mugabe's third Singapore visit this year.

Mugabe had been scheduled to address a campaign rally on Friday, but organizers say that has been cancelled due to the trip.

The opposition, which has called him a "non-resident president" due to his frequent foreign travels, has expressed concern over his health, saying he should retire.

Mugabe has said he will contest next year's election, claiming he is still fit. He has been in power since 1980.