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LONDON, ENGLAND - SEPTEMBER 15:  Fireman talk within the police cordon at Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism.  (Photo by Jack Taylor/Getty Images)
LONDON, ENGLAND - SEPTEMBER 15:  Fireman talk within the police cordon at Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism.  (Photo by Jack Taylor/Getty Images)

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UK Raises terror threat level after London attack

As a manhunt intensifies to find the terrorists behind the London subway attack, the U.K. is raising its terror level. CNN's Matthew Chance reports.

UK Raises terror threat level after London attack

As a manhunt intensifies to find the terrorists behind the London subway attack, the U.K. is raising its terror level. CNN's Matthew Chance reports.