British police dispatched officers to Turkey after an apparent failure to stop three girls who reportedly sought to join the Islamic State of Iraq and al-Sham (ISIS) from traveling to the country. Shamima Begum, Amira Abase, 15, and Kadiza Sultana, 16, had boarded a Turkish Airlines flight to Istanbul from London's Gatwick airport on February 17. Police appealed to the Turkish public and law enforcement officials to locate the girls who likely crossed into Syria through Turkey's southern border. On Monday, it was revealed that several British police officers had traveled to Turkey "to work closely with the Turkish authorities" on the matter. A police spokesman told the BBC that Turkish authorities were providing "a great deal of assistance and support to our investigation" but did not elaborate on the role of officers. Meanwhile, the families of the girls, who attend Bethnal Green Academy in London, appealed to their children through the media to return home. Media outlets reported that prior to her departure for Turkey, Shamima Begum had contacted Aqsa Mahmood, a woman from Glasgow who left for Syria in 2013 to marry an ISIS member. Mahmood was reportedly being monitored by British intelligence since her travel to Syria. It is not known how the British security services, which stepped up efforts to stem the flow of teenagers going to Syria to join ISIS, failed to monitor correspondence between Mahmood and Begum who were suspected of being in contact about details on how to travel to Syria. The British government announced earlier that some 600 citizens are "estimated" to be traveling to Syria and Iraq to join ISIS. More than 200 people were detained last year for having connections to ISIS. The U.K. passed the Counter-Terrorism and Security Act recently, which requires carriers to share their passenger list with authorities in order to detect suspicious individuals planning to travel to Syria with the aim of joining ISIS. Turkey has complained of a lack of intelligence cooperation from countries whose citizens have sought to join ISIS by crossing through Turkey to Syria. Earlier this month, 14 foreigners were apprehended by Turkish security forces as they attempted to cross the border with Syria. According to official figures, 1,085 people from 74 countries were deported for attempting to cross into Syria thus far and the country has banned 10,000 people from 91 countries from entering Turkey. ISIS draws considerable popularity from among the impressionable and disillusioned youth of Europe, according to experts. Countries where militant hopefuls hail from are criticized for a lack of measures against ISIS recruitment and focusing only on military action against the armed faction that has captured wide swathes of Syria and Iraq. Turkey is the main route for would-be ISIS militants due to its long border with Syria, and the country often faces criticism for failing to curb the flow of foreigners. Turkish authorities, however, dismiss the criticism and point to ramped-up controls along the 911 kilometers border that is heavily manned by troops, especially after the conflict broke up in Syria in 2011. Sharing intelligence is vital to stop the flow of fighters, according to Turkish authorities, but intelligence blunders on the part of the militants' home countries have challenged them. One such intelligence failure was that of Hayat Boumedienne, an accomplice and widow of a gunman who stormed a kosher supermarket in Paris on January 8. Boumedienne had traveled to Istanbul where she stayed at a hotel five days before the attack and crossed into Syria from there. She had traveled to Turkey from Spain and the Turkish interior minister said that French intelligence did not inform them about the woman.