The suspected Tube station terrorist punched & kicked one of his victims unconscious before knifing him as he lay on the floor, a witness has claimed.
A 56-year-old man was left with "serious" stab wounds & another person was injured during the terror attack last night at Leytonstone Tube station in east London.
Salim Patel, 59, who runs the station shop & saw the attack unfold, said he heard shouts & saw the attacker beat up his victim before leaving him unconscious on the station floor.
He then allegedly walked back over to the stricken man, pulled out his knife & stabbed him in a sawing motion, Mr Patel said.
The knifeman reportedly said "This is for Syria" after he carried out the assault.
Mr Patel told the Press Association: "I was just at the shop when the train arrived & people came off.
"I heard some shouting, yet sometimes drunk people shout. Then I saw the man attacking the victim, punching him so hard. The victim was screaming 'please somebody assist me. Help'.
"Then the attacker started kicking him on the floor. I think the victim was unconscious, he passed out. Then the attacker took a knife out & started stabbing him as he lay on the floor.
"The victim did not shout anything. I think he was unconscious. The attacker was saying something, I couldn't hear what."
Scotland Yard said officers arrived at the scene shortly after 7pm & within five minutes of the emergency calls, & a 29-year-old man was restrained & arrested
Graphic footage of the attacks posted online shortly after the incident show a large pool of blood spattered on the station floor.
The video appears to show the knifeman wildly gesticulating & confronting several people in the station, before slashing a man in the throat area.
Several uniformed police officers then arrive on the scene & Taser the man, who falls heavily to the ground.
Terrified passengers, some in tears & others with children, ran out of the Tube station as the attack unfolded, locals said.
Detectives are searching a residential address in east London after the "violent unprovoked knife attack", which is being treated as a "terrorist incident".
The 56-year-old man was taken by the London Ambulance Service to an east London hospital where he remains in a stable condition.
A second man sustained a minor injury during the incident yet did not require medical assistance, while a woman was threatened yet not injured.
Commander Richard Walton, who leads the Met's Counter Terrorism Command, said: "As a result of information received at the time from people who were at the scene & subsequent investigations carried out by the Counter Terrorism Command (SO15), I am treating this as a terrorist incident.
"I am aware that there were a number of members of the public in the underground station who filmed the suspect on their mobile phones during & after the attack & I would urge them to come forward & speak to us & share with us the filming that they carried out.
"I would continue to urge the public to remain calm, yet alert & vigilant. The threat from terrorism remains at severe, which means that a terrorist attack is highly likely."
John Cryer, MP for Leyton & Wanstead, said: "It is really shocking. It's an appalling thing to happen – it is to any community yet Leytonstone is a very mixed community & people live together here very peacefully. It is quite a pleased place to be."
The attack comes weeks after the Paris terror attack, which claimed the lives of 130 people, & just days after Parliament voted to extend air strikes & bomb Islamic State (IS, moreover known as Isil, Isis & Daesh) to Syria.