AKIPRESS.COM - An American paramedic working for European security watchdog OSCE's monitoring mission in eastern Ukraine was killed and two others were injured on Sunday when their vehicle struck a mine, triggering a U.S. call for a transparent, timely investigation, Reuters reported.

The Organization for Security and Cooperation in Europe (OSCE) said the killing was the first death of one of its members while on patrol in Ukraine, where more than 700 international observers help report on a simmering conflict that has deeply strained relations between Russia and the West.

A 2015 ceasefire between Ukraine and Russian-backed separatists in the eastern part of the country is regularly violated, and Washington cites the conflict as a key obstacle to improved relations between Russia and the United States.

U.S. State Department spokesman Mark Toner said the killing underscored the increasingly dangerous conditions under which the OSCE mission operated, including grappling with "access restrictions, threats, and harassment."

"The United States urges Russia to use its influence with the separatists to allow the OSCE to conduct a full, transparent, and timely investigation," Toner said.

U.S. Secretary of State Rex Tillerson also spoke about the incident on Sunday with Ukrainian President Petro Poroshenko, who offered his condolences.

"This tragic incident makes clear the need for all sides - and particularly the Russian-led separatist forces - to implement their commitments under the Minsk agreements immediately," Toner said.

The Minsk peace agreement, brokered by France and Germany and signed by Russia and Ukraine in February 2015, calls for a ceasefire, the withdrawal of heavy weapons from the front line and constitutional reform to give eastern Ukraine more autonomy.

But since the deal the sides appear stuck in a stalemate broken periodically by sharp resurgences of fighting that Kiev and the Kremlin accuse each other of instigating.

Tillerson told Poroshenko that although Washington wanted better ties with Moscow, "Russia’s actions in eastern Ukraine remain an obstacle," the State Department said.