Intelligence experts estimate that the Islamic State extremist group has between 60 and 80 operatives planted in Europe to carry out attacks, the Dutch counterterrorism coordinator said Friday.

Dick Schoof said in an interview with The Associated Press that would-be fighters are also heeding messages from the militant group "asking them not to come to Syria and Iraq, but to prepare attacks in Europe."

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One result is that over the last six months the number of "foreign terrorist fighters" hasn't grown, he said, but the fact that they're not traveling "does not mean that the potential threat of those who would have traveled is diminished."

Schoof said military operations to oust the Islamic State from its self-declared caliphate in Syria and Iraq are scattering the extremist group's fighters and supporters.

This will probably lead to a gradual increase of refugees that will pose a danger to the national security of the Netherlands and other European countries, he said.

Schoof said even though the Netherlands hasn't been hit by a major attack by Islamic extremists such as those in Belgium and France, "the chance of attack in the Netherlands is real."

"We have seen 294 terrorist fighters go overseas in Iraq and Syria and there are still 190 over there," he said. "And what happened in France and Brussels and Germany could happen to us."

There are probably between 4,000 and 5,000 European "foreign terrorist fighters" in Iraq and Syria, Schoof said.

While the number from the Netherlands, a nation of 17 million people, may seem low, he said, "whether there's 190 or 350, I think the number is big enough to worry."

Schoof, who was in New York to speak at a roundtable on "returning foreign terrorist fighters," said the Netherlands' program to deal with the threat balances "repression and prevention" and relies on strong cooperation between local and national authorities.

On the "repression" side, he said, fighters returning from Syria or Iraq are taken into custody and prosecuted, and courts have recently handed down six-year prison sentences in several cases. The government also takes away passports, freezes assets, and has beefed up security measures and the police force, he said.

On the prevention side, Schoof said, there's a lot of family support, with local authorities deciding the best interventions and providing education and psychological help if needed -- but there also could be arrests.

Jozias van Aartsen, the mayor of The Hague, said building trust and having close relations with the Muslim community is very important.

"They are Dutch citizens," he said. "There are some in the Netherlands who say shut down mosques. That's absolutely wrong policy."

But Van Aartsen said there is a need for vigilance. "The apparatus of local government can be very important as a watchdog against radicalization," he said.

Schoof stressed that the Netherlands does not tolerate "anti-democratic behavior."

"We try to prevent hate preachers coming in by not giving them a visa," he said.

The government is also concerned about the development of an ultraconservative strain of Islam known as Salafism, he said.

Last week, Schoof said, the Federation of Mosques, without any urging, sent a letter to all mosques in the country saying "the mosques themselves must realize that hate speech should not be accepted in the mosques."

"Those are important signals that you can build on in your trust relationships," he said.