(Reuters) - One member of European security watchdog OSCE's monitoring mission in eastern Ukraine was killed and two others were injured after their vehicle drove over a mine near Luhansk.
An American man was killed and a German woman was injured on Sunday morning, a spokesman for Austria's foreign ministry said. Austria holds the rotating presidency of the Organization for Security and Cooperation in Europe (OSCE).
Germany's foreign ministry said two were injured, but gave no immediate details. The OSCE confirmed on Twitter that a patrol with six members and two armored vehicles had been in a "serious incident" but gave no further information.
Three years after Moscow annexed the Crimean region, tensions between Ukraine and separatists in the Russian-held eastern part of the country remain high and a 2015 ceasefire agreement is violated regularly.
The Ukrainian military said the incident took place at 10:17 local time (3.17 a.m. ET) near the small village of Pryshyb, which is controlled by pro-Russian separatists.
The unarmed, civilian OSCE mission with more than 700 international observers was deployed in 2014. The role of the monitors includes verifying the withdrawal of heavy weapons as agreed under the 2015 ceasefire agreement.
German Chancellor Angela Merkel said she was appalled by the news and her government expected the parties to the conflict to investigate carefully and determine who was responsible.
"The conflict parties must also finally implement the long-agreed ceasefire," Merkel said in a statement. "And there, the Russia-supported separatists, who are illegally and violently occupying parts of Ukrainian territory bear a particular responsibility."
German Foreign Minister Sigmar Gabriel, in a separate statement, said it was in everyone's interest to allow the OSCE observers to "carry out their important, indispensable, and at once difficult and dangerous work.
Ukrainian President Petro Poroshenko and Austrian Foreign Minister Sebastian Kurz on Twitter both called for an investigation of the incident. Kurz said he had spoken to the mission's ambassador, Ertugrul Apakan.
"Need thorough investigation; those responsible will be held accountable," Kurz said on Twitter.
A spokesman for the OSCE said further information would be released as it became available.
The 57 member states of the OSCE, which include Ukraine, Russia and the United States, in March extended its monitoring in Ukraine by a year.
Gabriel said the OSCE patrols had clearly prevented a more serious military escalation in recent years.
(Reporting by Brenna Hughes Neghaiwi in Zurich, Francois Murphy in Vienna, Pavel Polityuk in Kiev and Andrea Shalal in Berlin; editing by Jason Neely)