“Increasingly more people are travelling to the training centres there from Germany,” Freiberg, the head of GdP trade union, told daily Passauer Neue Presse. “A large number have now returned and live here.”

These people have serious combat training, are radicalised, and want to carry out attacks, he told the paper.

“The number of dangerous Islamists lies at more than 100,” Freiberg said, adding that about 40 had received explosives training in terrorist camps.

Freiberg’s comments were in direct contrast to those by German Interior Minister Thomas de Maizière on Monday, who said that there was no reason to change the country’s security threat level in response to US and UK travel alert warning of possible terrorist attacks in Europe.

While de Maizière also said Berlin was taking all leads seriously and investigating them with high intensity, Freiberg complained that German police forces were not in a position to conduct surveillance on all of the perceived threats.

“Around-the-clock observation is not possible due to a personnel shortage,” he told the paper. “We’re running up against our limits.”

Terror threats should always be taken seriously, Freiburg said, adding that he regretted that “the cases where Germany has been able to prevent attacks have not been judged realistically enough.”

DAPD/ka