A car belonging to the OSCE’s Special Monitoring Mission to Ukraine (SMM) exploded after driving over a mine in the self-proclaimed Lugansk People’s Republic in the country’s east. One of the monitors was killed, the organization’s chairman has confirmed.

The OSCE’s current chairman, Austrian Foreign Minister Sebastian Kurz, tweeted his condolences after the incident.

He also said one person had been injured in the blast.

He also called for a thorough investigation, adding that “those responsible will be held accountable.”

The mission tweeted that the car had been involved “in a serious security incident in the Luhansk region.”

The OSCE car had strayed from its route, according to Sputnik news agency, citing the LPR press service.

“We know that the mentioned crew deviated from the main route and moved along side roads, which is prohibited by the mandate of the OSCE SMM,” the press service reported, as cited by the news agency.

The blast was “strong enough to penetrate an armored vehicle,” an unnamed OSCE official was quoted as saying by AFP.

The explosion was initially reported by a local militia, which also said one person had been killed. The car reportedly drove over a mine near the village of Prishib.

Both the Ukrainian military and anti-government forces were observing a ceasefire at the time of the incident, according to the Ukrainian representative of the Joint Center for Control and Coordination (JCCC).

“The Ukrainian side expresses condolences to the families of the victims,” the JCCC’s press service said in a statement on Facebook.

The OSCE’s SMM to Ukraine was deployed in March of 2014 to observe and report on the situation in the east of the country and facilitate dialogue between all parties involved in the ongoing conflict there.

The mission has previously come under fire at least seven times since the beginning of 2017, its representative told Sputnik.

This is the first time a monitor has been killed.

The conflict in eastern Ukraine broke out in the spring of 2014 after a wave of deadly protests led to an armed coup that ousted the elected government in Kiev. The new government sent troops to the Lugansk and Donetsk regions, which were unwilling to recognize the coup-installed authorities. The turmoil has claimed the lives of nearly 9,800 people since then, according to the Ukrainian Ministry of Foreign Affairs.