The U.S. envoy for efforts to end the Ukrainian conflict, Kurt Volker, is set to meet with Kremlin aide Vladislav Surkov on November 13 to explore deploying United Nations peacekeepers to eastern Ukraine.

Volker has said he would meet Surkov in Serbia’s capital, Belgrade, for a “discussion of principles” to see if they can agree on what a peacekeeping force might look like.

“We are not in agreement on this yet,” he told reporters in Washington on November 3.

Fighting between Kyiv government forces and Russia-backed separatists who hold parts of Ukraine’s Donetsk and Luhansk regions has killed more than 10,000 people since April 2014. Several cease-fire deals announced as part of the Minsk accords -- September 2014 and February 2015 pacts aimed to resolve the conflict -- have reduced fighting but not stopped it.

Alexander Hug, the principal deputy chief monitor of the Organization for Security and Cooperation in Europe's Special Monitoring Mission (OSCE SMM) to Ukraine, said last week that 425 civilians have been killed or injured in the conflict since the beginning of this year, according to Ukrainian media. Thirty-nine of them were children.

In a tweet on November 12, Volker said the civilian casualty toll for 2017 is "outpacing 2016" and added: "People of Donbas deserve a real ceasefire."

Russian President Vladimir Putin in September proposed deploying UN peacekeepers on the contact line separating the sides of the conflict to protect monitors from the OSCE.

The plan 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 said Washington wants the mission to monitor the entire conflict area and make sure heavy weapons are pulled back.

Putin later said he was open to adjustments to his initial proposal, but no agreement has been reached.

Ukrainian President Petro Poroshenko's office said on November 4 that he held a telephone conversation with U.S. Secretary of State Rex Tillerson during which they “coordinated further steps for the deployment of an international UN mission” in the separatist-held parts of Luhansk and Donetsk, including the border between those areas and Russia, which Kyiv says is used to ship weapons and military personnel in from Russia.

Volker last met Surkov on October 7 in Belgrade. The venue of the talks was not disclosed, although Serbian media said the two men met at a hotel.

Belgrade is a neutral venue. Volker had refused to meet with Surkov in Russia, and Surkov is barred from the European Union under sanctions imposed in response to Russia's aggression against Ukraine.

The two held talks for the first time on August 21 in the Belarusian capital, Minsk.

Tillerson appointed Volker, a former U.S. ambassador to NATO, as the U.S. special representative for Ukraine negotiations in July.

With reporting by Bloomberg