Kurt Volker, the U.S. special envoy for efforts to end the conflict in eastern Ukraine, has met with Crimean Tatar leaders Ilmi Umerov and Akhtem Chiygoz, who were released from custody in their Russian-occupied homeland this week.
Volker met with the two Tatar leaders in Kyiv on October 28, where they arrived the previous day.
Umerov and Chiygoz -- deputy chairmen of the Mejlis, the Crimean Tatar self-governing body that has been outlawed by Russian authorities -- were unexpectedly released and flown to Turkey on October 25, thanks partly to an intervention by Turkish President Recep Tayyip Erdogan.
They have vowed to return to Crimea to campaign for the release of other prisoners.
Volker, who arrived in Kyiv on October 27, said the release of Umerov and Chiygoz was a good sign, but said Russia should follow up with more positive moves in eastern Ukraine as well.
Russia seized Ukraine's Crimean Peninsula and fomented opposition to the central government in eastern Ukraine, where the ensuing war between Kyiv's forces and Russia-backed separatists has killed more than 10,000 people.
"The fact that they were released is a small positive sign," Volker told Reuters. "It's the kind of thing you hope you could build on that, Russia would build on that with some other steps with the [eastern region of] Donbas," he added.
Volker, who is a former U.S. envoy to NATO, was appointed in July by President Donald Trump's administration to help resolve the conflict.
Russia's involvement in eastern Ukraine is seen by Washington as a key obstacle to better relations between the United States and Russia.
Ukraine and the West also disagree with Russia's position on whether and how the United Nations should send a peacekeeping force to the region.
Russian President Vladimir Putin last month proposed deploying UN peacekeepers on the contact line separating the sides of the conflict -- a plan that swiftly drew criticism from both Kyiv and the West, in part because of concerns that deployment only along the front line would cement Russian control over separatist-held territory.
Volker met Kremlin aide Vladislav Surkov earlier this month for talks on the issue, which he said produced no breakthroughs but were "constructive."
"What we are doing, is we are seeing whether we can create some common ideas for how a peacekeeping force could be useful in resolving the conflict," Volker said, adding that peacekeepers could only be effective under a stronger mandate than Russia proposes.
Russia has denied sending troops or modern armament to the separatists in eastern Ukraine.
Volker said Russian aggression is responsible for the war in the east, but that Moscow could change its position once it understands the conflict is counterproductive for its own interests.
"The real issue is Russia's decision-making. Until now, Russia has been holding this territory, keeping this conflict alive, hoping that it provides some leverage over Ukraine," Volker said.
"The reality has sunk in I believe that this has actually produced the opposite. It has produced a Ukraine that is more unified, more nationalist, more anti-Russian, more westward-looking than ever existed before."
Volker also said Washington was "actively considering" supplying lethal defensive weapons to Kyiv, a move strongly opposed by Russia.
"No one has any worry about someone defending themselves unless they are an aggressor, so it should not be that controversial an issue," Volker said.
On October 27, Volker met with Ukrainian President Petro Poroshenko and Prime Minister Pavel Klimkin.
With reporting by Reuters, RFE/RL's Ukrainian Service, and Interfax