Ukraine opened a terror investigation Monday into a mine blast that killed an American medic from the Organization for Security and Co-operation in Europe's monitoring team in the country's rebel-held east.
The OSCE suffered its first casualty in the three-year war in Europe's backyard after an armoured vehicle hit a landmine Sunday in the Russian-backed separatist fiefdom of Lugansk.
An unidentified US medic was killed and two others, German and Czech nationals, were wounded as they travelled on a patrol monitoring the conflict that has claimed more than 10,000 lives.
The local branch of Ukraine's SBU security service in the conflict-hit Lugansk region said in a statement that it was treating the blast as an "act of terror that led to the loss of life."
The incident occurred in an insurgent-controlled part of the region and the separatists themselves have not yet said whether they intend to probe the circumstances under which the OSCE vehicle ended up driving over a landmine.
A spokesman for the Russian-backed Lugansk rebel police force told AFP that the vehicle hit an anti-tank mine.
An AFP photographer saw the mangled remains of the vehicle -- its floor ripped open and engine blown out of the hood -- being hauled away from the scene for further investigation.
The incident sparked sharp words toward Moscow from both Washington and Berlin.
The US State Department's acting spokesman Mark Toner said "the incident makes clear the need for all sides -- and particularly the Russian-led separatist forces -- to implement their commitments" under a long-ignored peace deal signed in February 2015.
"The United States again calls upon Russia to use its influence with the separatists to take the first step toward peace," Toner said.
German Chancellor Angela Merkel said in a statement that "the separatists supported by Russia who illegally occupy part of Ukrainian territory by violence have a special responsibility" to respect the 2015 agreement.
Both Kiev and the West accuse Moscow of plotting and backing the fighting in reprisal for the February 2014 ouster of Ukraine's Kremlin-backed leadership.
Russia denies this and in turn accuses the US State Department of fomenting the 2013-14 street protests that ended up allying ex-Soviet Ukraine with the West.
The OSCE team's 600 unarmed members in eastern Ukraine are the only independent monitoring mission in the devastated industrial war zone.
The group said the death would not deter it continuing to operate in Europe's only war zone.