The Organization for Security and Cooperation in Europe's (OSCE) monitoring mission confirmed on Wednesday that four civilians were killed in the shelling of a border checkpoint in eastern Ukraine.
Four people were killed, an unconfirmed number of people were injured and three vehicles were damaged, according to the mission's preliminary assessment.
The incident took place near the Elenovka checkpoint of the self-proclaimed Donetsk People's Republic.
Pro-Russian separatists said the victims were in their cars hoping to cross the checkpoint at the time of the attack.
The OSCE has said that fighting between the separatists and Ukrainian government troops has increased in recent weeks despite a year-old peace agreement.
According to a United Nations report, at least 9,000 people have been killed and 21,000 injured since violence erupted in eastern Ukraine in 2014.