France Bans 6 From Leaving Country

France barred six nationals from leaving the country on Monday, using a new law that aims to crack down on citizens traveling to Syria and other conflict zones to join militant groups.

Travel bans are becoming a key plank in government efforts to stem the flow of Western nationals to Syria and other conflict zones, where officials fear they are being further radicalized.

“Upon their return they represent an even greater danger for the country,” said French Interior Minister Bernard Cazeneuve. The minister said the government is preparing travel bans for an additional 40 nationals under the law, passed in November.

The French law ranks among the tougher measures introduced by governments across Europe that are struggling to track potential radicals.

The security risks were thrown into stark relief in January when Islamist militants unleashed deadly attacks across Paris and, more recently, in Copenhagen.

French authorities say at least one of the brothers who sprayed the newsroom of Charlie Hebdo with gunfire traveled to Yemen where he received weapons training from an al Qaeda offshoot.

Another gunman, Amedy Coulibaly, pledged allegiance to Islamic State in a video,sending the woman he married in a religious ceremony to Syria just days before he gunned down a policewoman in one attack and four shoppers at a kosher grocery in a separate assault.

In the U.K., the government is under scrutiny after three teenage Muslim girls slipped out the country less than a week after the government adopted measures aimed at curbing travel to Syria.

The U.K.’s Counter-Terrorism and Security Act makes it easier for border officials to confiscate the passports of suspected radicals. The law also grants authorities new powers to temporarily bar British citizens from returning to the U.K. if they are suspected of fighting alongside militant groups.

“Whenever there are concerns, police at the border should be alerted so they can use the new temporary passport seizure powers to stop people traveling,” British Prime MinisterDavid Cameron said Monday.

But the travel restrictions aren’t airtight. The three girls from East London—Kadiza Sultana, 16 years old, and Shamima Begum and Amira Abase, both 15—boarded a flight to Istanbul last Tuesday, according to police. Authorities say they believe the school friends were destined for Syria.

Weeks before the girls left the country, police say they had become aware of their links to another British national suspected of traveling to Syria.

Mr. Cameron expressed concern that teenagers could board a flight unaccompanied by adults—without being questioned by the airline.

“We need new proportionate arrangements with airlines to ensure that these at-risk children are properly identified and questioned,” Mr. Cameron said.

WSJ