Washington's first priority in dealing with the war in Ukraine is to reach agreement on a UN peacekeeping force, US Secretary of State Rex Tillerson said Wednesday.
Speaking a day ahead of planned talks with Russia's Foreign Minister Sergei Lavrov, Tillerson said he hoped to convince Moscow to allow a blue helmet force with a robust mandate.
"We prioritise ending the violence, that's our first priority, and to seek to do that we need to put a peacekeeping force in place," Tillerson said.
Russia has brought forward a proposal for a UN force to protect OSCE truce monitors deployed in eastern Ukraine where Russian-backed rebels are fighting Kiev's troops.
But Western powers fear that President Vladimir Putin is seeking to limit the force's mandate in such a way that any ceasefire would simply consolidate his allies' gains.
"Russia has long resisted a peacekeeping force, but they have agreed now," Tillerson told reporters after talks with NATO allies in Brussels.
"I think it's significant that we're talking about the right thing," he said.
But he warned that there was a "significant difference" over the mandate the force will have "and that's why we continue to talk with the Russians."
Tillerson is due in Vienna on Thursday for talks with the Organization for Security and Cooperation in Europe and US officials say he is expected to meet Lavrov there.
"We hope that we can close those gaps, we think it's vitally important to stop the violence. People are still dying every day," he said.
The OSCE has deployed 600 unarmed monitors in Ukraine to investigate and deter ceasefire violations, but they often come under fire from the warring factions.
One observer, an American, was killed in April 2017 in eastern Ukraine when his vehicle hit a landmine.