Police said they arrested a 19-year old man at Heathrow airport on Saturday on suspicion of "preparing for acts of terrorism" in relation to Syria.
The man is being held at a police station in London and an address in the north of the city is being searched, the Metropolitan police said in a statement.
Officers from the Counter Terrorism command unit made the arrest but police said it was not in response to any immediate risk or threat.
They said the arrest was "Syria-related" but no further details were available.
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