Story highlights The American is a paramedic, the OSCE said

The monitors work daily in a "dangerous security environment"

(CNN) An American paramedic attached to a monitoring patrol in volatile eastern Ukraine was killed in an explosion on Sunday, the Organization for Security and Co-operation in Europe said.

The US citizen was part of a patrol of the OSCE Special Monitoring Mission to Ukraine. It is the first time an SMM patrol member has been killed while on duty, OSCE Secretary General Lamberto Zannier said . The group has not released the victim's identity.

Two other monitors were injured in the incident, when their vehicle was heavily damaged by an explosion in the Luhansk region, near Pryshyb.

In one of the most thankless, obstructed, threatened, harassed monitoring missions in the world, first OSCE monitor killed today https://t.co/EWdVD3YtAP — Samantha Power (@SamanthaJPower) April 23, 2017

The OSCE is investigating the incident.

"This appalling incident underlines the increasingly dangerous security environment the SMM monitors are working in every day," Zannier said. "All sides are responsible for the safety and security of the OSCE monitors."

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