3 Missing Teenage Girls Now In Syria, British Police Say

British police say three teenage girls believed to have run away to join Islamist extremists have now crossed into Syria. The girls, ages 15 and 16, left their London homes Feb. 17 and boarded flights for Istanbul. Police think they then crossed the border into Syria hoping to join up with militants from the so-called Islamic State.

In a statement, U.K. Counter-Terrorism Commander Richard Walton said, "We are extremely concerned for the safety of these young girls." The police said they are working with Turkish authorities but would not provide further details.

Amira Abase and Shamima Begum, both 15, and Kadiza Sultana, 16, attended the same school in East London. Police say they are friends with another teenage girl who arrived in Syria in December.

Authorities believe the three girls were radicalized through online propaganda, and their case has ignited concerns about the teenage girls being lured to Syria to become young brides for Islamist fighters.

According to The Associated Press, British Prime Minister David Cameron said the girls "appear to have been induced to join a terrorist group that carries out the most hideous violence and believes girls should be married at nine and women should not leave the home."

Cameron has urged social media firms to be more aggressive in dealing with online extremism.

Scotland Yard says the families of the three girls are both surprised and devastated by their disappearance and have issued direct appeals to return home.

Abase Hussen, said his daughter, Amira, told him she was going to a wedding the day she left home, and that she was behaving normally. He urges his daughter to "Please think twice. Don't go to Syria."

Halima Khanom urges her sister, Kadiza, to find "the courage in your heart to contact us and let us know you're OK."

Renu Begum tells her younger sister, Shamima, that her mother needs her "more than anything else in the world."