A new public relations war raged Thursday between Moscow and Kiev after Ukraine deported a reporter with Russia's Channel One television for allegedly running "destructive" stories about the crisis-torn ex-Soviet state.

Ukraine's State Security Service (SBU) said it had expelled Alexandra Cherepnina for basing one of her stories on a home video in which a Ukrainian child was shown performing a Nazi salute and wielding a knife while calling for the murder of Russians.

The SBU said Thursday it had decided to "block the destructive actions of Channel One's journalist" and bar her from re-entering the country for three years.

A spokesman for Russian President Vladimir Putin denounced the expulsion as "completely unacceptable".

"Unfortunately, Ukraine has long since turned into a place where it is both hard and dangerous for reporters to work," spokesman Dmitry Peskov told reporters in Moscow.

"Unfortunately, we are witnessing a complete intolerance for pluralism in Ukraine," he said.

The airwaves on which Channel One operates have featured a news show called Vremya (Time) that was must see TV for generations of Russians and Soviets alike.

The channel led Wednesday's Vremya programme with an 11-minute report about the deportation.

It featured a phone interview with Cherepnina from the plane taking her back to Moscow in which she described being deprived of a chance to call anyone by the SBU after being detained.

The SBU agents "told me that I could have been the one who shot the (child) video and then presented it as if it was made by someone else," Cherepnina told the station.

- 'You cannot conceal truth ' -

The girl's purported family members in the video ask the child one question in Russian and another in Ukrainian -- an unusual combination for what Channel One said was a household of ultranationalists.

Moscow and Kiev have been waging a furious propaganda campaign through their state -- and some private -- media outlets designed to discredit the other and win over domestic support.

Russian television portrays the leadership that ousted a Kremlin-backed president last year as a "fascist" regime whose rise to power was part of a well-funded US effort to win the allegiance of vital ex-Soviet countries with close Moscow ties.

Kiev and its Western allies fight back with footage purporting to show Russian soldiers and weapons involved in the separatist conflict that has killed 6,500 people in east Ukraine in the past 15 months.

Russia denies any involvement in the war but provides the rebels with humanitarian support and diplomatic backing at frequent UN Security Council debates.

Moscow's powerful Investigative Committee -- a domestic security agency that answers directly to Putin and is often compared to the US FBI -- said it had launched an "illegal deprivation of liberty" probe into the incident.

"The current Ukrainian authorities will never understand that you cannot conceal the truth by intimidating and killing reporters," committee spokesman Vladimir Markin said in a statement.

"But the impunity with which the current Ukrainian authorities are acting will not last forever," Markin added.

"They will have to answer for everything, including their crimes against reporters," he warned.