The incident took place on the territory controlled by the self-proclaimed Lugansk People's Republic (LPR).
"We can confirm that an #OSCE patrol has been involve in a serious security incident in the Luhansk [Lugansk] region," the mission said on Facebook.
The OSCE mission in Ukraine car exploded on a mine in Donbass, the OSCE chairman, Sebastian Kurz, said.
"Tragic news from #Ukraine: SMM patrol drove on mine. One #OSCE patrol member killed, one injured 1/3." Kurz wrote on Twitter.
Kurz also called for a "thorough investigation into the incident." Those responsible will be held accoutable, he said. The OSCE chairman also expressed "heartfelt condolences" to the family of the killed OSCE staff member and the special monitoring mission in Ukraine team.
The press service of the LPR told Sputnik that the OSCE car deviated from the route it was supposed to follow.
"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 LPR press service specified.turmoil since April 2014, when the government in Kiev launched a military offensive against militia in Donbass. Despite the Minsk peace agreements signed in February 2015, the sides continue to blame each other for ceasefire violations.
The OSCE SMM to Ukraine was deployed in March 2014 to observe and report on the situation in the country.
This March, the SMM spokesperson told Sputnik that the observers of the OSCE Special Monitoring Mission (SMM) on Ukraine had been shelled at least seven times since the beginning of the year.