Imams have said the man who allegedly shouted "this is for Syria" before stabbing someone at a London Tube station was not known to them, adding "only he can answer" questions about his motives.
The attacker stabbed one man, wounding him critically, and injured two others at Leytonstone Underground Station in East London on Saturday evening.
Graphic footage of the attacks later emerged online, showing the knifeman appearing to slash a man in the throat, and blood pooled on the station floor.
He apparently shouted "this is for Syria" and "all your blood will be spilled" before being subdued by officers who fired a Taser. Police have confirmed they are investigating it as a terrorist incident.
A bystander was filmed shouting: "You ain't no Muslim bruv! You're an embarrassment." The hashtag #YouaintnoMuslimbruv circulated on Twitter as Londoners rallied to distance the man, whose religion is unknown, from Islam.
Imran Patel, from Leytonstone Islamic Association, told reporters on Sunday they were "saddened" by the attack.
"This was an individual who we do not know and is not a member of the congregation of Leytonstone. His motives for his actions, only he can answer for himself, he said.
"We strongly condemn any sort of violence or terrorism or any violent acts. Islam does not allow place for violence and terrorism.
"Leytonstone is a well-integrated and multi-cultural community, who live in peace and harmony. What happened last night is totally unacceptable and we totally and strongly condemn this."
Scotland Yard said officers arrived at the scene within five minutes of the emergency calls and a 29-year-old suspect was detained, The Press Association reports.
Detectives are currently searching a residential address in east London after the "violent unprovoked knife attack".
Salim Patel, 59, who runs the station shop and witnessed the attack, said: "I was just at the shop when the train arrived and people came off.
"I heard some shouting, but sometimes drunk people shout. Then I saw the guy attacking the victim, punching him so hard. The victim was screaming 'please somebody help 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 and 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."