MOSCOW (Reuters) - A Russian state television reporter was killed in Ukraine and his colleague is missing after their position was shelled in clashes between Ukrainian forces and pro-Russian separatists near the eastern city of Luhansk, the Rossiya-24 channel said on Tuesday.

Mr Igor Kornelyuk, 37, died in hospital after coming under fire while covering heavy fighting that began overnight when Ukrainian forces made a push to enter the main city in Ukraine's easternmost province, near the border with Russia, it said. "He was critically wounded in a mortar attack," the channel said on its website. "The fate of the sound man, Anton Voloshin, is unknown."

The Russian Foreign Ministry said Mr Kornelyuk's death demonstrated the "criminal nature" of Ukraine's military operation against pro-Russian rebels and urged the authorities in Kiev to investigate.

The loud crack of heavy artillery is audible on shaky footage shot by cameraman Viktor Denisov, who survived the attack on a rebel roadblock where they were filming.

As smoke clears, a fighter is shown dragging a wounded man off the road into the bushes. "I got lucky," Mr Denisov told the Russian LifeNews website. "One of the shells landed on them... I ran the other way when the area came under fire."

A spokesman for separatists in Luhansk said fighting was still too heavy to allow a search for Mr Voloshin.

Last month, an Italian photographer and his Russian translator were killed by mortar fire.

The crisis in Ukraine erupted late last year when protesters took to the streets against a president sympathetic to Moscow. He was overthrown in February, Russia annexed the Crimea region in March and the uprising in the Russian-speaking east began in April.

After his election at the end of May, President Petro Poroshenko ordered a military push to retake territory controlled by rebels.

Kiev says 125 Ukrainian service personnel have been killed. Scores of rebel fighters have also died, as well as an unknown number of civilians.