As a result of five years of bitter conflict, dozens of prisoners have been held by the two ex-Soviet countries.

Here are the high-profile prisoners involved in the swap.

Film director Oleg Sentsov is the most prominent of the Ukrainian prisoners held by Russia.

In 2015, he was sentenced to 20 years in a Russian Arctic penal colony on terror charges after a trial that Amnesty International likened to a Stalin-era show trial.

During court appearances, he remained unbroken, often smiling, singing the Ukrainian anthem and making defiant comments.

Sentsov, 43, opposed Russia's 2014 annexation of Crimea, where he lived.

He was sent to a strict-regime penal colony on the remote Yamal peninsula where he spent 145 days without solid food last year, demanding the release of all Ukrainian political prisoners.

His severe health problems and support from international film stars including Johnny Depp did not cause the Kremlin to budge.

Another Ukrainian, Alexander Kolchenko, who was convicted as Sentsov's co-defendant with a lower sentence, was also picked for release.

Vladimir Tsemakh, an alleged air defence specialist for pro-Russian separatists who Dutch investigators have described as a key witness in the downing of flight MH17, was also part of the exchange.

Ahead of the exchange, Dutch investigators questioned Tsemakh in Kiev this week, an informed source told AFP. Investigators consider him a "witness", not a "suspect", the source added.

A journalist for Russia's state-funded RIA Novosti news agency, 52-year-old Kyrylo Vyshynsky was detained last year in Kiev and charged with "high treason" in the interests of Moscow. He has dual Ukrainian and Russian citizenship.

Russian coastguards captured 24 Ukrainian sailors off the coast of Crimea in November last year after seizing their three vessels.

The crew includes 22 sailors and two agents of Ukraine's SBU security service.

Moscow had wanted to put them on trial for violating Russia's maritime borders.

Stanislav Klykh, 45, is a history professor while Mykola Karpyuk, 55, is a senior member of two Ukrainian nationalist protest groups.

They were arrested in Moscow in 2014 and handed lengthy sentences for fighting against Russian armed forces in Chechnya in the 1990s. Both men said they confessed after being tortured.

Pavlo Gryb, a 21-year-old blogger, is the youngest Ukrainian prisoner. Kiev said he was kidnapped by Russian special forces in Belarus where he went to visit a friend.

Russia sentenced him to six years in prison after finding him guilty of inciting a friend to carry out a bombing.

Roman Sushchenko, 50, was Paris correspondent for Ukraine's Ukrinform national news agency.

He was detained while on holiday in Moscow and last year sentenced to 12 years for espionage after he was accused of serving in Ukrainian military intelligence and gathering Russian state secrets.

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