Rainer Wendt, head of the union, told the website of daily paper Bild: “It is only a question of time before violent left-wingers attack a politician.”

He said the level of violence shown among left-wing activists was increasing. “The entire appearance of the new violent left-wing criminals is like the spirit of the RAF and their fight against the German state.”

But his comments were firmly contradicted by the Interior Ministry, from which a spokesman said: “There is no current knowledge of the existence of a left-wing terrorist organisation.”

He also said that, “Crimes with the aim of assassinating people,” were considered to be, “unlikely.”

But Wendt said he was convinced of the threat. “Those who do not stop at arson attacks on cars and houses, and throw Molotov cocktails at policemen, they see the lives of people as cheap,” he said.

He added that there were clear parallels to the RAF heydays in the 1970s. “The willingness to use violence, the hatred of the state and the social-revolutionary ideals of the violent left-wingers are the same,” he said. “And the methods such as arson attacks are the same as the RAF.”