The deaths of two Russian journalists killed in a mortar attack in eastern Ukraine was caught on film by their cameraman.

Igor Kornelyuk, a 37-year-old correspondent for Russian state-owned TV channel Rossiya 24, and sound engineer Anton Voloshin came under fire as they were reporting from a checkpoint held by pro-Russian insurgents in Mirny, near the city of Luhansk.

With them was cameramen Viktor Denisov, who filmed the attack.

The footage starts with the cameraman trailing a separatist militiaman taking cover behind an armoured vehicle that blocks the road.

Suddenly, mortar shelling starts to strike the site. During a break, an insurgent is seen dragging an injured man out of the fire line into the bushes at the side of the road.

Moments later, another blast hits the area.

Kornelyuk was rushed to a hospital, where he died after surgery. Voloshin reportedly died on site.

The deaths were followed by a late night telephone call between Ukrainian President Petro Poroshenko and Russia's Vladimir Putin to discuss a ceasefire in the eastern Ukraine.

The conversation resulted in Ukraine proposing a unilateral ceasefire to allow pro-Russian separatists a chance to lay down their weapons.

Denisov said Rossiya 24's crew was reporting on refugees fleeing the troubled area near the border with Russia, which has been at the heart of heavy fighting between pro-Russian militia and the Ukrainian military.

The UN and OSCE have called for a thorough investigation into the circumstances of the attack and said those responsible should be held accountable.

"This death is yet another horrid reminder that not enough is being done to protect journalists who risk their lives reporting from conflict zones in Ukraine," OSCE Representative on Freedom of the Media Dunja Mijatović said.

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Ukraine's UN ambassador, Yuriy Sergeyev, said Poroshenko expressed condolences to the families of the Russian journalists and said authorities were probing the incident.

Sergeyev added that Kornelyuk wasn't wearing the prescribed armoured vest and helmet identifying him as a journalist when he was hit.

Only at the hospital was it determined that he was a journalist, Sergeyev said.

"It is not clear if he entered Ukraine legally or not, but he didn't follow the instructions to all the journalists to be accredited. They didn't follow that so they performed at their own risks," Sergeyev said.

The ambassador said that government forces were fighting back at "terrorists" who attacked their positions near Luhansk. Ten insurgents were killed and many injured.

Kornelyuk is the fourth journalist to be killed in Ukraine since the start of the year.