LONDON (AFP, Reuters) - British police are investigating as a "terrorist incident" the stabbing of three people at a London Underground train station on Saturday (Dec 5), 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 group (ISIS) 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 Leytonstone 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 (3:06am Singapore time) 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.

The Leytonstone incident will draw parallels with the May 2013 murder of British army soldier Lee Rigby, who was hacked to death just south of the Thames River by two Muslim converts.

Britain is on its second-highest alert level of "severe", meaning a militant attack is considered highly likely, mainly because of the threat posed by Islamic State (ISIS) militants in Syria and Iraq who are encouraging supporters to attack the West.

After ISIS militants claimed responsibility for the attacks on Paris last month that killed 130 people, British Prime Minister David Cameron won approval from lawmakers on Wednesday to bomb the Islamist group in Syria.

British warplanes first bombed oil fields controlled by Islamic State on Thursday.

THREAT TO BRITAIN?

Cameron said air strikes would not increase the chances of an attack on Britain, since militants already viewed Britain as a top target with seven plots foiled over the past year.

An eyewitness to the knife attack was quoted as saying the attacker had screamed about Syria. "I just saw a lot of people running but I ignored it and kept walking to get my train, but suddenly what I saw, I couldn't believe my eyes and what I saw was a guy with a knife,"the Guardian quoted an eyewitness as saying. "As he was coming out this is what he said: 'This is what happens when you f*** with mother Syria, all of your blood will be spilled.'"

Such apparently random attacks are extremely difficult to thwart because they require relatively little planning and very basic equipment.

In 2013, Michael Adebolajo and Michael Adebowale ran over Fusilier Rigby near Woolwich Barracks before setting upon him with knives and a meat cleaver in an attempt to behead him.

They asked bystanders to film them with bloodied hands, calmly justifying their actions as a response to Britain's foreign policy. They were jailed for life last year.

British security services say about two-thirds of their time is spent countering international militants, much of that connected to Syria.

Britain's worst militant Islamist attack came in July 2005, when 52 people were killed by suicide bombs on underground trains and a bus. A beach attack in Tunisia in June this year killed 30 British holidaymakers, the biggest loss of British lives in such an incident since the July 2005 bombings.

ISIS said on Saturday that the married couple who killed 14 people in a mass shooting in California, which US authorities are investigating as an act of terrorism, were followers of the militant group.