A knifeman slashed a man's throat at a busy London tube station and allegedly shouted 'this is for Syria' before being tazered by police.
The victim suffered serious knife injuries at Leytonstone underground station shortly after 7pm.
Eyewitnesses claimed they could hear 'this is for Syria' and 'all of your blood will be spilled' during the terrifying attack.
After slashing his victim's throat, the man allegedly threatened several other passengers before being confronted by a number of un-armed police officers.
The officers ordered the man to drop his weapon, who continued to wave the large knife.
After refusing to drop his knife, one officer tazered the suspect, who dropped to the ground.
A number of police raced to the man and quickly handcuffed him.
A Scotland Yard spokesman said: 'Police were called at 19:06hrs on Saturday, 5 December, to reports of a stabbing at Leytonstone underground station. The male suspect was reportedly threatening other people with a knife.
'Met officers attended the scene. A man was arrested at 19:14hrs and taken to an east London police station where he remains in custody. A Taser was discharged by one of the Met officers.
'Officers from British Transport Police are now dealing with the incident at the scene. We are aware of one man having sustained serious stab injuries. We await details of any other injuries.'
The Metropolitan Police has refused to comment on whether the attack was related to extremism.
By Darren Boyle, Jay Akbar, Tom Wyke, Martin Beckford, and Stephen Adams
