Ukrainian President Volodymyr Zelensky has called on world leaders to respond after a video emerged apparently showing a Ukrainian soldier being beheaded by a Russian serviceman.

“Everyone must react. Every leader. Do not wait for this to be forgotten,” he said in a video address.

Ukraine’s SBU security service said it was investigating the “war crime”.

The Kremlin said the video was “awful” but its authenticity had to be checked as well as who was behind it.

The grainy and extremely graphic video appears to have been filmed on a mobile phone, and possibly during the summer months. It shows a man in military uniform wearing a yellow armband – frequently worn as identifying symbols by Ukrainian soldiers.

The perpetrator and other men visible in the clip have white bands on their legs, which Russian soldiers are known to wear as a means of identification.

Video frames showing a yellow armband and white cloth leg wrapping used by Ukrainian and Russian soldiers respectively

They can also be heard to speak Russian, although that is not conclusive as many Ukrainians speak Russian too.

During the short video, the victim with the yellow armband is beheaded by a man with a large knife who is wearing a white band around his leg.

At one point, one of the men holds up body armour with a trident mark – the state symbol of Ukraine.

The colours and shape of the trident badge are similar to the insignia of the Ukrainian ground forces.

The body armour also features what looks like the Punisher skull symbol (a comic-book character), which in the current conflict has been spotted being worn by fighters on both sides.

A green passport-like booklet is also visible on the ground. It’s upside down in the video (highlighted below) but its appearance matches that of the standard-issue Ukrainian military ID in its colour, the presence of a Ukrainian trident symbol and the layout of the writing.

There has been speculation online that the video was filmed near the city of Kreminna in eastern Ukraine.

The BBC has been unable to verify these claims as the video’s surrounding features offer too few visual clues to identify its location, such as buildings or specific landscape points.

It also remains unclear when the footage was filmed. It looks as if it’s from the current conflict, where white and yellow armbands have been used by opposing sides as identification.

The leaves In the video are bright green which suggests that it may have been from late spring or summer last year.

Some social media users have suggested it may have been filmed in July but we cannot verify this.

The footage began circulating on Telegram late on Tuesday, after a popular pro-Kremlin blogger shared it with his nearly 300,000 followers.

He later claimed he was not the original source of the video and that the footage had been on Telegram before he posted it. We have been unable to find any earlier versions.

The video has since spread to Twitter.

Kremlin spokesman Dmitry Peskov said that “in the world of fakes that we inhabit, we need to check the veracity of this footage”.

Another video purporting to show the bodies of two beheaded soldiers has also been circulating on social media in recent days.

The video shows what appears to be a destroyed M113 armoured personnel carrier, mainly used by Ukrainian forces. A man filming the scene says in Russian that it had driven over a mine. At least two bodies without heads and hands can be seen lying on the ground nearby.

A yellow armband Is visible on the right arm of one of the bodies, suggesting the victims had been fighting on the Ukrainian side. At least three other soldiers can be seen standing over the two bodies.

Social media comments have suggested the video was filmed near Bakhmut, where Russian forces – including the Wagner private military company – have been battling Ukrainian troops for control of the city.

However, the BBC has been unable to verify the location of the video.

Wagner founder Yevgeny Prigozhin has put out a statement saying that he has “not found” any evidence that the events in the video had happened near Bakhmut or involved Wagner fighters.

Many gruesome videos have been posted online since the war began.

Last month President Zelensky promised to find the Russian soldiers who apparently shot dead an unarmed Ukrainian prisoner of war named Oleksandr Matsiyevskiy.

EU foreign affairs spokeswoman Nabila Massrali reminded Russia it had to abide by humanitarian law and added that the EU was committed to holding to account all perpetrators of war crimes committed during the war. (BBC)

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