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, 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.
The official said 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 2018 elections during a one-day special congress on Friday.
The security official would not say how Mugabe was traveling although the privately owned NewsDay newspaper said he was on a state-owned Air Zimbabwe plane.
Mugabe was granted immunity from prosecution and assured of his safety under his resignation deal, a source of frustration to many Zimbabweans who accused him of looting state coffers and destroying the economy during his time in power.
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