Ukrainian President Petro Poroshenko says he has ordered his government to "immediately" resume talks with Moscow on the release of Ukrainian citizens from Russian custody following a prisoner swap between Kyiv and Russia-backed separatists.
Visiting the Odesa region on December 28, Poroshenko said Kyiv "will do everything we can" to return all Ukrainians held in Russia or "as hostages in occupied territory" -- a reference to Crimea and separatist-controlled parts of eastern Ukraine.
"We cannot betray them. We cannot forget them," he said.
Earlier in the day in Kyiv, Poroshenko said that his government did not release any Russian citizens in the prisoner swap on December 27, which was the largest such exchange since the war in eastern Ukraine began in April 2014.
"We will do more to get our citizens out of Russian jails...and because of that not a single Russian national was released by us now," he said, hinting that Kyiv would only agree to release Russians in Ukrainian custody in exchange for Ukrainians held in Russia.
On December 1, Ukrainian Ombudswoman Valeria Lutkovska said more than 2,000 Ukrainian citizens remain in Russian custody.
On December 28, the United States said it welcomed the long-awaited swap of prisoners and called on both sides to commit to a true “all-for-all” detainee exchange.
In March, the European Parliament called on Russia to free more than 30 Ukrainian citizens who were in prison or other conditions of restricted freedom in Russia, Crimea, and parts of eastern Ukraine that are controlled by the Russia-backed separatists.
Poroshenko named several Ukrainians held in Russia, including filmmaker Oleh Sentsov and journalist Roman Sushchenko.
Sentsov is serving a 20-year prison term, while Sushchenko is being held in Russia on suspicion of espionage. Kyiv says the charges against both men are fabricated.*
In the December 27 swap, Ukraine handed 233 captives over to the Russia-backed separatists in the eastern Ukrainian regions of Luhansk and Donetsk, while the separatists handed 74 Ukrainian nationals over to Kyiv.
After massive protests pushed Moscow-friendly Ukrainian President Viktor Yanukovych from power in February 2014 following his decision to scrap a landmark deal with the European Union, Russia seized control of the Crimea region and fomented separatism across eastern and southern Ukraine.
The Russia-backed separatists seized parts of the Donetsk and Luhansk regions, igniting the war -- which has killed more than 10,300 people and continues despite a 2015 deal on a case-fire and steps toward peace -- and severely straining Russia's relations with Kyiv and the West.
*CORRECTION: This story has been updated to clarify that Roman Sushchenko has not been tried or sentenced; he is being held in Russia on suspicion of espionage.
With reporting by UNIAN and Ukrayinska Pravda