18-year-old was apprehended by the counter-terrorism command at St Pancras International station
A man suspected of preparing an attack was arrested on Tuesday as he was trying to leave Britain from a central London train station served by Eurostar, police said.
The 18-year-old was apprehended by the counter-terrorism command at St Pancras International station, from where Eurostar trains depart to continental destinations including Paris and Brussels, London's Metropolitan Police said.
"He was arrested on suspicion of preparation of acts of terrorism, dissemination of terrorist publications and inviting support for a proscribed organisation," the police said in a statement.
"This arrest does not relate to offences against the UK," police said, adding that a search was under way at a home in north London.
The police did not reveal the man's nationality or where he was trying to travel to.
A spokesman for Eurostar told AFP he had "no information" about the arrest.
The police operation comes less than two weeks after a terror attack on British parliament which killed four people and left dozens injured.