Russia refused to proceed with an exchange of prisoners unless Ukraine agreed to hand over a key witness in the 2014 downing of flight MH17, a senior Ukrainian official said.
Vladimir Tsemakh, believed to be an air defense specialist for pro-Moscow rebels in eastern Ukraine, arrived in Moscow on Saturday as part of a historic prisoner exchange between the two ex-Soviet countries.
The Dutch government expressed regret that Ukraine had handed Tsemakh over to Russia, saying it had tried to prevent it.
Tsemakh was reportedly in charge of air defense in the area where the MH17 came down.
"Tsemakh's absence from the exchange list automatically meant the cessation of talks with Russia," Ivan Bakanov, the head of Ukraine's SBU security service, told the Interfax-Ukraine news agency.
Bakanov described Moscow's insistence on his release as "proof of Russia's involvement in the MH17 crash".
He said the Ukrainian government had no "moral right" to put off the swap any longer.
"As a state, Ukraine is showing the world that it is saving its citizens like the world's strongest democracies," he said.
Ukrainian President Volodymyr Zelensky said on Saturday that Tsemakh had been questioned before being sent to Russia.
"We've done everything. Everything we've been asked to do. It was complicated. I was afraid that the exchange may fall through because of this," Zelensky said.
The Dutch government contacted Ukraine "several times and at the very highest level" in an effort to prevent the handover of Tsemakh, Foreign Minister Stef Blok said in a letter to parliament.
Blok said the authorities had the opportunity to question Tsemakh before he left for Russia but the Netherlands still profoundly regretted the outcome.
Flight MH17 from Amsterdam to Kuala Lumpur was shot down by a Russian-made missile in July 2014 over eastern Ukraine, killing all 283 passengers and 15 crew onboard, two-thirds of them Dutch.