Ukraine's government on Thursday swapped prisoners with Russia-backed separatists in the war-torn east of the country, ahead of Orthodox Easter celebrations.

Twenty people who had been held captive in two breakaway regions were handed over to the government, Kiev said.

Separatists took back 14 prisoners but three others refused to return, Ukrainian President Volodymyr Zelensky's office told AFP.

"I'm happy every time we get our citizens back: our heroes, soldiers, political prisoners and ordinary citizens of Ukraine," Zelensky said in a video address.

"We will fight until all Ukrainians come home."

Alevtina Popova, the only woman among those handed to Ukraine, said she had been detained by separatists for providing help to Ukrainian servicemen in 2018, in a video released by Zelensky's office.

She said she was feeling "relief" after the exchange and was ready to undergo the mandatory two-week coronavirus quarantine.

Ukraine's ombudsman, Lyudmyla Denisova, said the lockdown imposed in Ukraine to control the coronavirus epidemic had made prisoner exchange talks "much harder".

Denisova added that another 200 prisoners were still being held by separatists and 115 Ukrainians were being held in Russia and Moscow-annexed Crimea.

Ukraine's ally Washington welcomed Thursday's swap.

In a statement on Twitter, the US embassy in Kiev called on Russia "to immediately release all other Ukrainians who remain unjustly imprisoned".

The foreign ministers of France and Germany, whose countries act as mediators in Ukraine's peace talks, also hailed the move, calling the swap "an important step" towards the conflict settlement.      

"The humanitarian value of the release of people detained in time of conflict cannot be underestimated," the International Committee of the Red Cross said in a statement.

"It is also essential that, even in the time of COVID-19, detainees continue to be released and are able to finally see their families again."

United Nations Secretary General Antonio Guterres welcomed "this important humanitarian action" which he hopes "will serve as a positive step towards more progress, including a permanent ceasefire", his spokesman said in a statement.

The Ukrainian presidency announced the swap deal last week.

Ties between Ukraine and Russia were shredded after the popular 2014 uprising ousted a Kremlin-backed president in Kiev. 

Russia went on to annex Crimea and support separatists in eastern Ukraine. Since then, more than 13,000 people have been killed in the conflict.