Daesh terrorist group has issued a video showing the beheading of what it described as a Russian intelligence officer captured in Syria, the U.S.-based SITE monitoring website reported on Tuesday.

The Russian Defense Ministry and the FSB security service were not immediately available for comment.

The 12-minute Russian-language video, released on the day Russia celebrates the anniversary of the 1945 victory over Nazi Germany with military parades, showed the man dressed in a black jump suit, allegedly Colonel Evgeny Petrenko, kneeling in a desert scene and urging other Russian agents to surrender.

"This idiot believed the promises of his state not to abandon him if he was captured," a narrator says in the recording, before a bearded man beheaded him with a knife.

The authenticity of the recording and the identity of the man could not immediately be verified, nor was it clear when the killing occurred.

Meanwhile, Russia's defense ministry denied on Tuesday that a Russian serviceman had been captured and executed by the Daesh group in Syria, Russian news agencies reported. The ministry did not reply to a Reuters request seeking comment.

Russian forces are backing Bashar al-Assad's regime in the war with the opposition and extremist groups seeking to oust him. The video showed scenes of what it described as the aftermath of Russian bombing raids in Syria.

The Russian defense ministry says about 30 Russian servicemen have been killed since the start of the Kremlin's operation there in September 2015.