Security footage appears to show three British schoolgirls, believed to be on their way to join Islamic State militants, waiting for hours at a bus station in Turkey before traveling to a city near the Syrian border, media reported on Sunday.

British police and the girls' families have issued urgent appeals for their daughters to return home after they flew to Istanbul from London on Feb. 17. Friends Amira Abase, 15, Shamima Begum, 15, and Kadiza Sultana, 16, are thought to have since entered Syria, British police have said.

European governments have called on Turkey to stem the flow of foreign fighters to Syria, and British Prime Minister David Cameron has urged social media firms to do more to deal with online extremism, saying the girls appeared to have been radicalized "in their bedrooms."