Terrorist Threats

‘‘Syria has become really the predominant jihadist battlefield in the world.’’ The international Herald Tribune disclosed on July 29, 2013.

The daily added that a  rising number of radicalized young Muslims with Western passports are traveling to Syria to fight with the terrorists against the Syrian government, raising fears among American and European intelligence officials of a new terrorist threat when the fighters return home.

More Westerners are now fighting in Syria than fought in conflicts in Iraq, Afghanistan, Somalia or Yemen, according to the officials, citing the  growing concern that they will come back with a burst of jihadist zeal, some semblance of military discipline, enhanced weapons and explosives skills, and, in the worst case, orders from affiliates of Al Qaeda to carry out terrorist strikes.

Classified estimates from Western intelligence services and unclassified assessments from government and independent experts put the number of fighters from Europe, North America and Australia who have entered Syria since 2011 at more than 600. That represents about 10 percent of the roughly 6,000 foreign fighters who have poured into Syria by way of the Middle East and North Africa.

Most of the Westerners are self-radicalized and are traveling on their own initiative to Turkey, where “rebel” facilitators often link them up with specific groups, terrorism experts say. Many have joined ranks with the Qaeda-aligned Nusra Front, which American officials have designated as a terrorist group.

European and other Western intelligence agencies are rushing to work together to track the individuals seeking to cross the border into Syria from Turkey, though several American officials expressed frustration that Turkey is not taking more aggressive steps to stem the flow of Europeans going to fight in Syria.

The German authorities have so far focused domestic efforts on preventing people suspected of being radicals from leaving the country. In the northern state of Schleswig-Holstein, the security authorities this month identified 12 people thought to be radicals, who they said had given ‘‘concrete indications’’ that they were planning to leave for Syria.

Public prosecutors in the Netherlands have said that while the authorities cannot stop would-be jihadists from leaving the country, they can combat recruitment, which is against the law and carries a sentence of up to four years in jail or a fine of about $100,000.

A precise breakdown of the Western fighters in Syria is difficult to offer, counterterrorism and intelligence officials said, but their estimates include about 140 French citizens, 100 Britons, 75 Spaniards, 60 Germans, and a few dozen Canadians and Australians. There are also fighters from Austria, Belgium, Denmark, Finland, Ireland, Italy, Norway, Sweden and the Netherlands, according to a study in April by the International Center for the Study of Radicalization, a partnership of academic institutions that is based in London estimated that 140 to 600 Europeans had gone to Syria.

About 30 French citizens have returned from the front lines in Syria, according to Mathieu Guidère, a professor at Université Toulouse II and an expert on Islamic terrorism.

Recently, the Dutch authorities arrested a 19-year-old woman suspected of recruiting young Dutch Muslims to fight with Islamic extremists in Syria.

In April, the Belgian authorities raided 48 homes across the country and detained six men implicated in what prosecutors described as a jihadist recruitment drive for the insurgency in Syria. Some of the men have since been released, Eric van der Sypt, a spokesman for the federal prosecutor, said by telephone on Friday.

Mr. van der Sypt said the Belgian authorities had recently arrested another man after he returned to Belgium from Syria, but he declined to provide more information, citing the continuing investigation.

‘‘We’re still following the phenomenon of people going to Syria from very close by,’’ he said, referring to residents who had become involved in a radicalist group known as Sharia4Belgium, in places like Antwerp and Vilvoorde, a community north of Brussels.

 Dr. Mohammad Abdo Al-Ibrahim