British police are investigating as a "terrorist incident" the stabbing of three people at a London Underground train station on Saturday, which left a pool of blood in the ticket hall.
One eyewitness at Leytonstone station shouted "You're no Muslim" at the lone male suspect as he was pinned down by police officers, amateur video footage showed.
The attack came at the end of a week in which the British parliament voted to extend air strikes on the Islamic State militant group from Iraq into Syria.
Britain's Counter-Terrorism Command is investigating the stabbings.
"We are treating this as a terrorist incident," CTC leader Commander Richard Walton said in a police statement.
One man was arrested following the incident at the suburban east London station.
Amateur video circulating on the Internet showed a pool of blood and bloody footprints at the Tube station ticket gates.
Some commuters continued on their journey while others briskly jogged away from the scene.
Shouts are heard as the suspect is seen remonstrating with people before swinging at one of them.
Footage shows an officer shouting "Drop the knife!" and firing a Taser electric stun gun.
A later clip shows the man being pinned to the ground by police as passers-by are told to get back.
One man at the scene shouted: "You ain't no Muslim, bruv! You're no Muslim, bruv! You ain't no Muslim!"
Police said they were called at 7:06pm (1906 GMT) to reports of a number of people being stabbed at the suburban station on the Central Line.
"The male suspect was reportedly threatening other people with a knife," Scotland Yard police headquarters said.
"A man was arrested at 7:14pm and taken to an east London police station where he remains in custody.
"One man has sustained serious knife injuries; these are not believed at this stage to be life-threatening. Two other people have sustained minor injuries."
Walton said: "I would urge the public to remain calm, but alert and vigilant."
The London Ambulance Service said: "We have treated one patient for stab wounds this evening at Leytonstone Underground station.
"The patient was taken to hospital escorted by the doctor from London's Air Ambulance."
The Central Line, which runs across the capital, was shut for several stops east from Liverpool Street Station -- the main overground London railway terminus serving eastern England and London Stansted Airport.