Following a meeting with Kremlin aide Vladislav Surkov in Dubai on Friday, special envoy Kurt Volker said he had conveyed to his Russian counterpart "a very strong sense of disappointment and frustration"."

"Russia has done absolutely nothing to end the conflict" between Ukraine government forces and Kremlin-backed rebels in the east of the country, Volker said.

The fighting has already cost more than 10,000 lives since April 2014

"This is something that has been noticed and is source of frustration in Washington," Volker underlined during a press briefing via conference call from New York.

Friday's meeting with Surkiv was the fourth between the two men about the conflict in Ukraine since Volker was appointed as the State Department's special representative in July 2017.

US President Donald Trump's envoy noted that Moscow has finally demonstrated "more openness in thinking about a wider mandate" and "wider geographic area" for the United Nations peacekeeping mission, an issue widely discussed in recent months.

Earlier Russian President Vladimir Putin had only backed establishing an armed mission along the front line splitting the insurgent-controlled territories from the rest of Ukraine.

The Kremlin categorically opposed positioning armed UN peacekeepers along the uncontrolled part of its border with Ukraine, which is not under Kiev's control.

"The Russian side is going to come back to us with a revised proposal," Volker told the media.

Early this month, German Foreign Minister Sigmar Gabriel said he wanted to establish a mandate for an armed UN peacekeeping mission in eastern Ukraine before Russia's March presidential election.

Kiev and the West accuse Russia of orchestrating the conflict in eastern Ukraine and of smuggling weapons and troops across the border. Moscow denies all the allegations.