Four Ukrainian civilians were killed when a minivan carrying them drove over a landmine as they waited to cross out of separatist-held territory in eastern Ukraine, authorities say.

Two passengers died instantly and two others later from their injuries from the explosion about 20 kilometres south-west of the rebel-controlled city of Donetsk.

"The minivan was queuing in the 'grey' area (between separatist and government-held territory)," a Ukrainian military spokesman said.

"Ignoring the signs warning about the danger of mines, the vehicle pulled out onto the roadside and there was an explosion."

One passenger survived the blast, he said.

There is still a substantial number of unexploded mines across the conflict zone, despite efforts to clear them.

Fighting continues despite a year-old ceasefire agreement.

Last week the head of the Organisation for Security and Cooperation in Europe (OSCE), which monitors the implementation of the ceasefire deal, voiced deep concern over escalating violence in eastern territories.

More than 9,000 soldiers and civilians have been killed since the conflict broke out in April 2014, when the pro-Russian separatists rose up following Russia's seizure of Ukraine's Crimea region.

Reuters