Russia’s defence ministry on Thursday announced that 55 of its servicemen had been returned to Russia.
The ministry said this was the largest prisoner exchange deal with Ukraine since the start of the war.
In its daily briefing, the ministry said the fighters from Russia’s armed forces and its proxies had been transported to Russia by a military plane and were undergoing medical checks.
The surprise swap involved almost 300 people, including 10 foreigners and Ukrainian commanders who had led a prolonged defence of the port city of Mariupol.
The Russian-installed separatist head of the self-proclaimed Donetsk People’s Republic, DPR, said that pro-Kremlin Ukrainian politician Viktor Medvedchuk had been freed as part of the deal.
Medvedchuk, a personal friend of Russian President Vladimir Putin, headed a banned pro-Russian party in Ukraine and was facing treason charges.
The swap was brokered by Saudi Arabia.
It came just before referendums in parts of Ukraine occupied by Russia that were likely to pave the wave for Russia to formally declare the annexation of more swathes of its neighbour.