A knife attack in a London subway station occurred on Saturday is being treated as a “terrorist incident,” police said after they arrested the 29-year-old man who is suspected of the assault.

The man wielding a knife slashed a man in Leytonstone Underground station, about 10 km east of central London on Saturday reportedly screaming “this is for Syria”.

A 56-year-old victim had sustained serious, but nonlife-threatening injuries, and two others were wounded less seriously.

The police officers detained the attacker using a Taser on him.

Police refused to comment on why the attack was being described and investrigated as a terrorist incident or on reports that the attacker had said that he was acting in response to Western involvement in Syria.

“I would urge the public to remain calm, but alert and vigilant,” Cmdr. Richard Walton, who leads the Counter Terrorism Command of London’s Metropolitan Police, said in a statement. “The threat from terrorism remains at severe, which means that a terrorist attack is highly likely.”

One person, who claims to have witnessed the attack, revealed details of the horror on Twitter. : “I was so scared I ran for my life. After good 10-15 police came and got the guy and arrested him.

“And 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.’”, The Guardian reports.