Ukraine and separatist rebels in the east of the country are carrying out the biggest exchange of prisoners since the conflict began in 2014.
Ukrainian authorities are transferring more than 260 people back to rebel-held areas, in return for 74 prisoners who have been held by pro-Russia rebels in the Donetsk and Luhansk regions.
It is the first swap in 15 months.
The release and exchange of prisoners was one of the points in the Minsk peace agreement, signed in 2015.
The deal has stalled since and analysts say the swap does not signify wider progress. Both sides continue to hold other prisoners.
Buses and other vehicles carrying the prisoners assembled at the Mayorsk checkpoint near the city of Horlivka in Donetsk for the swap.
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Originally, 306 prisoners were meant to be returned to rebel-held territory, but some have reportedly refused to go, for reasons that are as yet unclear.
The negotiations for the exchange saw the involvement of presidents Vladimir Putin of Russia and Petro Poroshenko of Ukraine, as well as the head of the Russian Orthodox Church.
The conflict in eastern Ukraine erupted in April 2014, soon after Russia annexed Ukraine’s Crimea peninsula. The UN says more than 10,000 people have died in the Donetsk and Luhansk regions.