Russia and Ukraine on Saturday exchanged 70 prisoners after intense negotiations.

Thirty-five people from each side, including 24 Ukrainian sailors who were detained in the incident near the Sea of Azov last November by Russia, and Russian journalist Kirill Vyshinsky convicted of espionage, were freed.

Commenting on the exchange, Ukrainian President Volodymyr Zelensky said it was the first step towards "unlocking a dialogue with Russia, and to an end of the conflict in the east of Ukraine".

"We agreed [with Russian President Vladimir Putin] on the first stage of unlocking our dialogue and ending the war. Today's exchange can be considered the first step in unlocking the dialogue with Russia," Zelensky said, adding that he discussed the issue with Putin in a phone talk on Saturday.

Russian Foreign Ministry spokeswoman Maria Zakharova called the detainees transfer "a very important step".

"It is necessary to support this attitude aiming to solve problems, and not to aggravate them as much as possible. Political will and systematic hard work bear fruit," Zakharova said on Facebook.

The two dozen Ukrainian sailors were detained by Russia during a naval incident late last year off the Crimean coast.

Relations between Russia and Ukraine have plummeted to an all-time low in recent years, since Moscow's 2014 annexation of Crimea in retaliation for Kiev ousting its pro-Russian president.

Talk of a prisoner-swap increased after Ukrainian President Volodymyr Zelensky came to power in May.

The exchange could be a significant step toward easing Russia-Ukraine relations and raising chances for resolving the conflict in Ukraine's east where fighting between troops and Russia-backed separatists has killed more than 13,000 people since 2014.

Yelena Gitlanskaya, a spokeswoman for Ukraine's SBU security service, told reporters at Kyiv's Boryspil airport that "the Russians have left," according to Russian state news agency Tass.

Russian news agencies also reported that a Ukrainian plane carrying released prisoners has taken off from Moscow's Vnukovo airport.

It wasn't clear who specifically was on board the Russian plane, aside from Kirill Vyshinsky, head of the Russian state news agency RIA-Novosti's Ukraine branch, who had been jailed since 2018 on treason charges. His presence was confirmed by Dmitry Kiselev, head of the Rossiya Segodnya media group that includes the agency.

Russian attorney Mark Feigin tweeted that prisoners from the Russian side include 24 Ukrainian sailors who were seized by Russia in November, along with Ukrainian journalist Roman Sushchenko who he has represented and filmmaker Oleg Sentsov, convicted of plotting terrorist acts.