A radical Ukrainian politician has claimed Queen Elizabeth drinks the blood of separatists’ babies in an apparent joke after she was pictured accidentally wearing the colours of the national flag.

Oleh Lyashko, dubbed a “vigilante” in the country for his filmed interrogations of rebels, posted a picture of the monarch on his Facebook page.

Taken during the Easter Sunday service at Windsor Castle earlier this month, she is seen smiling while wearing a pale blue outfit and holding a bunch of the bright yellow flowers.

Oleh Lyashko made the 'joke' on his Facebook page on Sunday

“Her Majesty Queen Elizabeth II. An aggressive, cynical (anti-Soviet) Bandera follower, a punisher granny, a loyal adherent of the Kiev junta,” Mr Lyashko's caption said, according to a translation by Russian state media.

“Her secret of youth is that she drinks fresh blood of DPR and LPR babies every morning.”

Buckingham Palace declined to comment.

The DPR and LPR are abbreviations of the “people’s republics” in Donetsk and Luhansk oblasts in eastern Ukraine, where separatists are in power following contested referendums last year.

The regions have seen more than a year of sporadic fighting between rebels and government forces in a conflict that has killed more than 6,000 people so far.

Oleh Lyashko has backed several extreme laws to crack down on separatist support in Ukraine (AFP/Getty Images)

Mr Lyashko is a member of the Ukrainian parliament and leader of the Radical Party, who received more than 8 per cent of the vote to come third in last year’s presidential elections.

He was singled out in an Amnesty International report for his “grim” self-publicised videos showing himself and accomplices appearing to abduct and interrogate people.

Monitors claimed he and armed men in his group known as the Lyashko Battalion illegally detain rebels and suspected supporters with “complete impunity”.

“Oleg Lyashko is supposed to be a lawmaker, but he has taken the law into his own hands,” the Amnesty report said.

Oleh Lyashko detaining a 'separatist' in July 2014 in a picture posted to his Facebook page (Oleh Lyashko/Facebook)

“’Glory to Ukraine, death to the occupiers’ is his rallying cry .Though he doesn't have the right to detain people, he abducts them and abuses them verbally and physically while the camera is rolling.”

A picture on his Facebook page in May showed him standing over a suspected separatist who had been stripped, bound, and loaded into the trunk of a car: “Today was a good day — we detained four terrorists. Glory to Ukraine!”

Mr Lyashko explained in an interview: “If I see a separatist, I consider it my personal obligation to detain him, because the fewer separatists there are the more peace there is.”