Russia and Ukraine carried out a long-awaited prisoner swap on Saturday in a step that could thaw a deep freeze in relations since the conflict over eastern Ukraine erupted in 2014. 

After lengthy negotiations, expectations have been running high for the prisoner swap, which had been described as imminent by the leaders of both countries in recent days. 

On Saturday a Russian aircraft carrying freed Russian prisoners from Kiev landed in Moscow while a Ukrainian plane with released Ukrainian prisoners aboard touched down in Kiev. 

The swap was carried out on a "35-to-35" basis, Interfax news agency quoted Russian human rights commissioner Tatyana Moskalkova as saying.  

"Ukraine has handed out 35 people to Russia, we handed out the same number to Ukraine," she said. 

"We view the agreed mutual release of persons held in Russia and Ukraine as a positive signal that should be followed by other important steps to break the impasse in the current situation in Russia-Ukraine relations," the Russian Foreign Ministry said in a statement.

Ukrainian President Volodymyr Zelensky hugged and shook hands with the freed Ukrainians, saying the exchange of prisoners was the first step in a process to end the conflict in Ukraine's Donbass region. 

He said the swap had been agreed with Russian counterpart Vladimir Putin, and that he hoped for a meeting in the so-called "Normandy Format" with Ukraine, Russia, France and Germany soon to help defuse the war with pro-Russian rebels. 

Zelensky said all steps had to be taken "to finish this horrible war." 

All the 24 Ukrainian sailors detained by Russia in the Kerch Strait last year were part of the swap, according to their lawyer Nikolai Polozov said. On the other hand, Ukraine has included a man suspected of involvement in the downing of a Malaysia Airlines flight over eastern Ukraine in 2014 in the swap, the Dutch government said. 

Zelensky raised the prospect of a prisoner swap after sweeping to power in an election in April. The comedian-turned-politician, whose defeat of incumbent Petro Poroshenko shocked Ukraine's political elite, had vowed during the campaign to bring Ukrainian prisoners home. 

On Thursday, Putin said the "large-scale" prisoner exchange with Ukraine was being finalized and that the swap would be "a huge step towards normalizing relations" with Kiev.   

German Chancellor Angela Merkel on Saturday hailed the swap a "sign of hope" and called for the implementation of a 2015 ceasefire deal that Paris and Berlin helped broker.   

"This exchange of prisoners between Russia and Ukraine is a sign of hope... it's worth continuing the hard work to implement the Minsk accord," Merkel said in a statement put out by her spokesman Steffen Seibert on Twitter.  

"I am happy for the Ukrainian sailors and Oleg Sentsov who can finally return home," she said, referring to the most famous Ukrainian prisoner held in Russia. Sentsov was arrested in 2014 and had been serving a 20-year sentence for planning "terrorist attacks" in Crimea. 

French Foreign Minister Jean-Yves Le Drian welcomed the breakthrough, while urging "concrete new advances" by each side to end their five-year conflict.  

"It's a gesture that demonstrates the willingness of Russia and Ukraine to renew their dialogue," he said in a statement. "France, alongside Germany, will support efforts by both sides with the aim of making concrete new advances in the coming weeks." 

U.S. President Donald Trump welcomed the prisoner exchange Saturday as a potential step toward peace. 

"Russia and Ukraine just swapped large numbers of prisoners. Very good news, perhaps a first giant step to peace. Congratulations to both countries!" Trump tweeted.