LONDON » Prime Minister David Cameron of Britain said Saturday that the country’s authorities would do everything they could to help three British schoolgirls who were believed to be traveling to Syria to join the Islamic State militant group.

European officials say they are increasingly concerned by reports about Western Muslims who have shown an interest in joining radical Islamic groups in Syria and Iraq, including young women who want to either fight for groups like Islamic State or become the wives of jihadis.

Estimates from Europe’s counterterrorism coordinator suggest that more than 3,000 Europeans may have traveled to Syria and Iraq since early 2014, and could represent roughly one-quarter of the foreign fighters in the region.

Cameron said that the latest case, which involves three teenagers from London — Kadiza Sultana, 16; Shamima Begum, 15; and an unidentified 15-year-old girl — was "deeply concerning," and he called on community and religious groups to do more to stop the radicalization of young British Muslims.

"It does make a broader point, which is the fight against Islamist extremist terror is not just one that we can wage by the police and border control," Cameron said, referring to the disappearance of the three girls. "We all have a role to play in stopping people from having their minds poisoned by this appalling death cult."

The British police have appealed for information about the three girls, who flew to Turkey last week without informing their families and are thought to be traveling to Syria to join the terrorist group.

The teenagers told their families on Feb. 17 that they would be out for the day, but security camera footage at Gatwick Airport, near London, showed that the girls had boarded a flight to Istanbul, according to British police.

"We are extremely concerned for the safety of these young girls," Richard Waldon, commander of a British special operations police counterterrorism unit, said in a statement. "The choice of returning home from Syria is often taken away from those under the control of Islamic State, leaving their families in the U.K. devastated and with very few options to secure their safe return."

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