Germany’s domestic intelligence agency expects that Islamic extremists who have traveled to Syria and Iraq will return and commit terror attacks.

Unlike Britain, Germany hasn’t raised its national threat level for terrorism recently. But Hans-Georg Maassen, head of the Federal Office for the Protection of the Constitution, said in an interview broadcast Sunday that there was an “increased abstract threat” of attacks in Germany.

At least 400 people from Germany have gone to Syria and Iraq to fight with Islamic extremist groups, though the real figure may be significantly higher, Maassen told Deutschlandfunk radio.

“We have to assume … that there may well be people who return and commit attacks,” he said, adding that his agency is aware of at least 25 jihadists with combat experience who have already come back to Germany.

Maassen said that the Islamic State group, which has swept into northern Iraq from Syria in recent months, has huge appeal among Muslim extremists.

“(They are) far more attractive than Jabhat al-Nursa, the al-Qaida offshoot in Syria. What attracts people is their high brutality, their radicalism, their strictness,” Maassen said.

German news weekly Der Spiegel reported Sunday that there are about 20 former German soldiers among the jihadists who have left from Germany to fight in Syria. Citing unnamed security officials, Der Spiegel reported that they were former conscripts who are more valuable than untrained recruits for groups such as IS.

Maassen noted that his agency wants to improve its cooperation with Turkey, a key transit country for Europeans seeking to join extremist groups.

He cited the high number of Germans traveling to Syria, including at least five known to have committed suicide attacks, as “simply not acceptable from a German point of view.”

“I know the Turks are doing quite a bit, but we’re also in the process of improving our cooperating with Turkey on this issue,” he said.

(AP)