THE HAGUE, Netherlands (AP) — Dozens of Dutch citizens are fighting with rebels in Syria and could return home battle-hardened, traumatized and even further radicalized, the chief of the Netherlands’ top intelligence agency has warned.

In a rare interview with Dutch television aired late Thursday, Rob Bertholee, head of the General Intelligence and Security Service, said the number of Dutch nationals heading to Syria is growing fast and he is concerned about their return home after fighting with radical Islamic rebels in the civil war.

“In my view that is very worrying because of the combat experience they acquire, the ideological convictions and the fact that they could become traumatized there,” Bertholee told Dutch current affairs show Nieuwsuur.

There have been no terror attacks in the Netherlands for years, but authorities have warned of the growing risk of Muslims going overseas to fight for their faith and then returning home.

A terrorism expert said Friday that images of Syrian President Bashar Assad’s brutal crackdown on rebels is drawing fighters from not only the Netherlands but across Europe.

Peter Knoope, director of the International Centre for Counter-Terrorism in The Hague, said the real problems could emerge when the Syrian civil war finally ends. He said that after conflicts like the one in Syria, “You always have some sort of proliferation of fighters who go somewhere else. … They have been taught to fight, and some of them do not know how to stop.”

Like Knoope, Bertholee said the problem is not just a Dutch one. He estimated that hundreds of people from around Europe and dozens from the Netherlands have traveled to Syria to join rebels fighting what they see as a holy war to oust Assad.

In the only reported Dutch case of would-be jihadists, police in the port city of Rotterdam arrested three men in November on suspicion of preparing to travel to Syria to fight alongside rebels. The men, whose identities have not been released, are due in court next month.

The Dutch assessments came as France also expressed concerns about its citizens heading to Mali to join radical Islamic fighters there, even as the French army is fighting the Muslim rebels in its former colony.

French police arrested four youths this week suspected of trying to join radical Islamic fighters in West Africa, and expelled radical imams and others considered risks to public order.

Bertholee said propaganda romanticizing the civil war is helping draw foreigners into Syria’s maelstrom of violence, from which it may be hard to escape.

“I think many of the jihad fighters who go there realize very quickly it is less romantic than they were led to believe,” he said. “But at the same time they realize there is no way back.”

Copyright 2013 The Associated Press.