MOSCOW (AP) — At least five people including a pregnant woman were killed and more than 10 injured early Wednesday on the front line in eastern Ukraine in the worst civilian loss of life there in months, separatist officials said.

Fighting between Russia-backed separatists and Ukrainian government forces has been raging for two years, claiming more than 9,100 lives.

The hostilities have left large swathes of eastern Ukraine in rebel hands. Both the government and the rebels have set up checkpoints on the front line, leaving thousands of people queuing for hours if not days to cross from one side to the other. Travelers have to apply for permits and are subject to checks. Local residents have complained of hold-ups on both sides as well as corrupt Ukrainian officials making money on giving travelers a fast track.

Self-proclaimed officials in the east said on Wednesday the victims were spending the night in their cars at the checkpoint outside the village of Olenivka hoping to cross the line in the morning.

The rebels' Donetsk News Agency quoted defense chief Eduard Basurin saying that there was a pregnant woman among those killed. Basurin claimed the civilians were killed by artillery fire from the Ukrainian side.

Footage from the scene showed cars on the side of the road riddled with shrapnel and one of them overturned. Unidentified forensic experts were seen examining what appeared to be a crater from a mortar shell.

Ukrainian officials denied responsibility. The independent News of Donbass website on Wednesday quoted local border guard spokesman Anatoly Kotsurba as saying that there was a blast at the checkpoint but no artillery fire from their side.

International observers have decried the creation of de-facto border checks, which have left thousands of pedestrians and motorists queuing on the front line of the conflict, and warned of risks of holding civilians there.

Officials from both sides have had to close checkpoints regularly in the past months as fighting flared up along the front line.