The 10-member crew of the Russia's tanker was allowed to disembark and leave Ukraine since they were not involved in November's incident, Russian human rights ombudswoman Tatyana Moskalkova said. Russian ships fired on and seized the Ukrainian vessels on Nov. 25 in the Kerch Strait, located between the Black Sea and the Sea of Azov. Ukraine has insisted the vessels were in international waters when Russia intercepted them.
Officials in both countries, which already had strained relations, said earlier this month they were preparing a major prisoner exchange that would include the 24 Ukrainian crew members who were detained in November.
U.N. deputy spokesman Farhan Haq said the United Nations could not independently verify the circumstances surrounding the incident but "we reiterate the need to refrain from any ratcheting up of actions or rhetoric."
Ukrainian President Volodymyr Zelenskiy's office did not have immediate comment on the incident. Russian officials protested the tanker's seizure, saying it would dampen the chances of the prisoner swap.
"This is very bad news," Russian Deputy Foreign Minister Grigory Karasin told the state-owned RIA Novosti news agency Thursday. "Someone in Kiev wants a tough throwback to their own provocation on Nov. 25."
The Ukrainian Security Service, also known as SBU, is still led by an ally of Ukraine's former president, Petro Poroshenko, Zelenskiy called Russian President Vladimir Putin earlier this month for their first conversation since Zelenskiy took office in May. The Ukrainian president, who was a popular comedian before he won an April election, made securing the release of the Ukrainian sailors one of his first priorities.