Zimbabwe's former president Robert Mugabe has left the country for medical checks in Singapore, his first foreign travel since the army forced him from office last month, a state security official said on Tuesday.

The 93-year-old, who ruled the southern African nation for 37 years, resigned after the army and his ruling ZANU-PF party turned against him when it became clear that his 52-year-old wife, Grace, was being groomed as his successor.

Until recently the world's oldest head of state, Mugabe had a reputation for extensive and expensive international travel, including regular medical trips to Singapore - a source of public anger among his impoverished citizens.

He left Harare with Grace and aides on Monday evening, the official said. He is expected to make a stop-over in Malaysia, where his daughter, Bona, is expecting a second child.

"He has gone for a routine medical trip to Singapore," said the official, who has organised Mugabe's security protection but who is not authorised to speak to the media. "He was due for a check-up but events of the last few weeks made it impossible for him to travel."

The trip means Mugabe will not be in Zimbabwe when ZANU-PF endorses President Emmerson Mnangagwa as its leader and presidential candidate for next year's elections during a one-day special congress on Friday.