Four civilians were killed in shelling on three cars about half a kilometre from a rebel checkpoint in eastern Ukraine, the Organization for Security and Cooperation in Europe (OSCE), which independently monitors the conflict, said Thursday.
The shelling targeted the southern edge of the rebel-held town of Olenivka in the Donetsk region, the OSCE said in a statement, without attributing blame.
One car was an "upside-down, split-in-two burnt-out wreck," and the other two had significant shrapnel damage, the statement said.
"Action needs to be taken to make travelling across the contact line safer, including through demining, and to enable civilians to cross the contact line in more locations," the OSCE's Ukraine mission chief, Ertugrul Apakan, said in a separate statement.
Apakan noted that there has been a flare-up in fighting in recent weeks, with the reappearance of many weapons that had previous been withdrawn.
In New York, the UN Security Council held a briefing on the situation in Ukraine - its first formal meeting on the issue this year - at the request of Ukraine, which is currently on the council.
Most council members condemned Russia's continued support for pro-Russia separatists in the country's eastern region and expressed concern over the increasing number of ceasefire violations.
Samantha Power, US ambassador to the UN, warned that violence in eastern Ukraine is at its highest level since last September and said the current hostilities could be traced back to Russia's annexation of Crimea, which she called the "original sin."
Vitaly Churkin, Russia's UN ambassador, said that the Ukrainian crisis was provoked by a "coup d'etat with external support" and rejected claims that the source of conflict was "Crimea's union with Russia."
"No, you will not be able to convince us this way," Churkin said. "Crimea is a stable peninsula."
More than 9,000 people have died in the Ukraine conflict, according to estimates by the United Nations.
The conflict erupted in 2014 after Ukraine ousted its pro-Russian president amid a protest movement calling for closer ties with the West.