U.S. officials have been focused on the security threat posed by fighters heading to Syria from the United States, Canada and Europe.

U.S. Attorney General Eric Holder urged countries in Europe and elsewhere on Tuesday to do more to keep their own citizens from traveling to Syria to fight, saying the world cannot allow Syria to become a training ground for violent extremists.

In a speech in Norway, Holder said other countries could learn from U.S. efforts to conduct undercover sting operations and use laws against preparing to commit attacks, tactics he said have helped confront the threat in the United States.

Speaking at the U.S. ambassador’s residence in Oslo, Holder also urged Europeans to share information about travelers to Syria with the United States, which does not require visas for travelers from European Union countries.

“We have a mutual and compelling interest in developing shared strategies for confronting the influx of U.S.- and European-born violent extremists into Syria,” Holder said, according to prepared remarks.

The suggestions come as Islamic State militants have taken control of most of eastern Syria and built on the momentum of their advance through Sunni Muslim provinces of neighbouring Iraq.

U.S. intelligence agencies estimate around 7,000 of the 23,000 violent extremists operating in Syria are foreign fighters, including dozens of Americans, Holder said.

U.S. officials have been focused on the security threat posed by fighters heading to Syria from the United States, Canada and Europe.

Extremists have tried to recruit Westerners and send them back to their home countries with a mission. “Syria has become a matter of homeland security,” Homeland Security Secretary Jeh Johnson said in a February speech in Washington.

In May a 22-year-old from Florida carried out a suicide bombing in Syria’s Idlib province.

Earlier on Tuesday, Holder told reporters that federal prosecutors had opened fewer than 100 investigations into American citizens who may have traveled to Syria or Iraq to fight.
A Denver woman accused of trying to fly to Syria to support insurgents there was arrested last week, and two men in central Texas were arrested on similar charges last month.

One of the Texas men was charged with “attempting to provide material support to terrorists,” a law that Holder urged other countries to copy as vital to counterterrorism efforts.

Holder’s remarks came amid a weeklong trip to Europe, which includes another stop in London during which the Syrian foreign fighter issue is expected to dominate.

In Norway, Holder also held up a new plan in the country to try to prevent its citizens from turning to extremism, and told reporters he would consider implementing something similar in the United States.

Last week, reports surfaced of a Norwegian citizen who was earlier accused of threatening Norway’s royal family traveling to Syria and appearing in a jihadist video.

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