A man wielding a knife slashed a man in an east London underground station on Saturday, reportedly screaming "this is for Syria", before police used a stun gun to detain him in what they described as a terrorist incident.
A pool of blood near the ticket barriers at the Leytonstone Station, about 6 miles (10 km) east of central London, was visible in footage posted on Twitter that also showed the suspect confronting officers at just after 1900 GMT.
Police said initial reports indicated the man had also threatened other bystanders. One man had serious knife injuries that were not thought to be life-threatening and two other people had minor injuries, police said.