The Maldivian opposition leader and former president, Mohamed Nasheed, has left for the UK where he is due to have back surgery.
Nasheed's departure was delayed by a day after - according to his party - the government imposed new conditions on his trip.
Nasheed was given a 13-year sentence under anti-terror laws last year.
The Maldivian government said Nasheed had signed an undertaking to return after his treatment.
His brother has agreed to act as guarantor, it said.
The government had only agreed to his trip on Saturday following international pressure.
On Sunday his lawyers said the government was insisting that he nominate a family member to stay in the capital, Male, to guarantee his return.
They called this "blackmail".
However the Maldivian Foreign Minister Dunya Maumoon said it was "standard procedure" for any prisoner travelling abroad for medical treatment to sign a guarantee.
"All prisoners who have travelled abroad have signed such documents as required by Maldivian law," he said.
"This rule has been in existence before Mr Nasheed came to office, and has not been introduced in an ad hoc manner."
One of Nasheed's US lawyers, Jared Genser, tweeted that the jailed politician had spoken to US Secretary of State John Kerry by phone.
Nasheed was flying from Male to Colombo, AFP reported, and from there would fly to the UK.
A former human rights campaigner, Nasheed became the nation's first democratically elected leader in 2008, ending three decades of rule by former strongman Maumoon Abdul Gayoom.
In 2012, he was detained after being accused of ordering the arrest of a judge.
He resigned months later amid an army mutiny and public protests over the judge's fate.
Nasheed alleged that he had been removed by a coup, but this was denied by his vice-president, who replaced him.
The current President Abdulla Yameen was elected in controversial polls in 2013 and is the half-brother of Mr Gayoom.