Earlier in the day, UK Prime Minister Theresa May said that a British-born man inspired by Islamist ideology, who had been previously investigated by MI-5 is responsible for the attack.
"Our working assumption is that the attacker was inspired by Islamist ideology," May said.
She added that the Westminster attack perpetrator "was a peripheral figure."
London Metropolitan police said they were treating the events as terrorist incidents. The attack is currently being investigated.
Earlier on Thursday, eight were arrested in connection with the attack.