article_snippet: The arrest follows that of three teenagers from northwest London on Sunday after they were intercepted by Turkish police in Istanbul.
article_snippet: The investigation started Friday, after police learned the two 17-year-olds were missing and were believed to be traveling to Syria.
article_snippet: police learned the two 17-year-olds were missing and were believed to be traveling to Syria were traveling with a 19-year-old, police said.
article_snippet: British authorities shared intelligence regarding the 17-year-olds with Turkish officials Friday, and that night, British authorities landed in Istanbul on a flight from Barcelona, Spain, a Turkish official told CNN.
article_snippet: The teens were stopped with another person seen as suspicious by Turkish intelligence at the airport's risk analysis center, which monitors risky flights and runs checks on suspicious passengers trying to enter Turkey.
article_snippet: Turkish authorities questioned The teens, a Turkish official said, and the Metropolitan Police said the three returned to London shortly before midnight Saturday and were arrested.
article_snippet: Last week, Turkish authorities said Turkish authorities had arrested a  person -- working for an undisclosed nation's intelligence service -- on suspicion of helping three British girls who are thought to have entered Syria to join ISIS.
article_snippet: British police say British police think the three east London classmates -- Shamima Begum, 15; Kadiza Sultana, 16; and Amira Abase, 15 -- traveled to Syria after flying from London to Istanbul on February 17.