UPDATE: 6:35 p.m. EDT -- The British Counter-Terrorism Command is investigating the stabbing of three people in the London Underground Saturday as an incident of terrorism, according to a report in Agence France-Presse. "We are treating this as a terrorist incident," CTC leader Commander Richard Walton said in a police statement.

The suspect was threatening riders with a knife, officials said, but was later arrested and taken into custody. One man sustained serious knife injuries that were not believed to be life threatening, while two others sustained minor injuries, according to officials at Scotland Yard police headquarters. 

Amateur video footage circulating on the Internet showed a pool of blood and bloody footprints at the Tube station's ticket gates. The U.K. remains on high altert after the attacks in Paris last month that killed 130 people.

Leytonstone is a mainly low-income residential area with a large immigrant population from Asia and Eastern Europe, the Wall Street Journal reports. 

Original story:

A man in London Saturday stabbed another man in a train station, reportedly yelling, “This is for Syria,” as he attacked, the Express reported and various social media accounts noted. The man, who reportedly had a machete or knife, also threatened the lives of others at the Leytonstone station in East London, but police subdued the attacker with a Taser.

Police arrested the man and took him into custody. The victim was transported to a local hospital by an air ambulance. Details on his condition were not available immediately. 

The victim reportedly had injuries in the neck, where he was slashed by the suspect, the Mirror reported. Much information is still not available about the incident, but some witnesses have tried to detail the attack. 

"As I walked down I just saw a lot of people running, but I ignored it and kept walking to get my train, but suddenly what I saw -- I couldn't believe my eyes -- and what I saw was a guy with a knife and a dead guy on the floor,” said Laurynas Godvisa, who reportedly witnessed the scene, according to the Mirror. "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 Mirror quoted Godvisa as saying.

A graphic video that was reportedly taken after the incident shows a large amount of blood on the floor of the station. It's unclear exactly what the attacker meant by the Syria comment.

Earlier Saturday, the United Kingdom conducted a series of airstrikes in Syria to combat the Islamic State group, the BBC reported. The London attack comes amid heightened concerns over security after the Paris terror attacks last month, for which the group claimed responsibility, that killed 130 people.