More than 400 people have left Germany to join militant groups in Iraq and Syria, and at least five have died in suicide bombings, the chief of Germany’s domestic security agency said Sunday.

“We have to expect that these people will return and commit attacks here,” Hans-Georg Maassen, the chief of the Federal Office for the Protection of the Constitution (BfV), told Deutschlandfunk radio.

Maassen spoke of a “greater abstract risk” of attacks in Germany, but did not provide any concrete evidence.

On Friday, Britain raised its terrorist threat level to “severe” over the risk posed by militants in Iraq and Syria, and Prime Minister David Cameron said intelligence services believe at least 500 Britons have gone to fight in Syria and Iraq.

While Germany has not yet tightened its security measures, Maassen stressed the importance of intensifying cooperation with Turkish intelligence services, as many fighters transit through Turkey to fight in Iraq and Syria.

Earlier this year, BfV said that about 10 per cent of those travelling from Germany to Syria are converts to Islam, and that women made up 7 per cent of those making their way to Syria.  SAPA