One international observer with the European security watchdog OSCE has been killed and two other monitors wounded after their vehicle struck a landmine while on patrol in eastern Ukraine.

The six-member patrol consisting of two armoured vehicles from the Organisation for Security and Co-operation in Europe was travelling on Sunday in an area of the Luhansk region, which is not under control of Ukrainian authorities.

The nationalities of the victims were not immediately released. 

The Ukrainian military said the incident took place at 10:17am local time (07:17 GMT) near the small village of Pryshyb, which is controlled by Russia-backed separatists.

Sebastian Kurz, the Austrian foreign minister, who also serves as the OSCE's chairman, wrote on Twitter: "Death of colleague is a shock to whole OSCE."

He also called for a "thorough investigation" into who was responsible for the blast.

Sigmar Gabrial, German foreign minister, expressed concern about the killing.

"Someone who just wanted to help create peace and put an end to the fighting has lost his life today," Gabrial said.

Rebels comment

The de facto authorities in Luhansk told a local news agency, Luhanskinformcentre, the incident happened because the OSCE convoy made a diversion from its route, Russia's TASS news agency reported.

"It is known that the aforementioned crew deviated from the main route and was moving along secondary roads, which is prohibited by the mandate of the OSCE SMM. We repeatedly drew the attention of the OSCE SMM on the observance of the necessary security measures during monitoring travel routes," said the unidentified rebel representative.

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OSCE deployed a special monitoring mission to Ukraine in 2014, after conflict erupted between the Ukrainian government and Russian-backed rebels.

The 57-member states of the organisation - which include Ukraine, Russia, and the United States - extended the monitoring mission in Ukraine by a year in March.

The OSCE has 600 employees in the country.

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.

Source: News agencies