London ISIS attack: Investigation on to find more terror links

A joint investigation by Scotland Yard's counter-terrorism command and MI5 led to new arrests on Thursday in London, Birmingham and Manchester, in connection with Wednesday's terror attack in Westminster, with two people still in custody.

Properties were also searched in Wales and southern England, reports The Guardian.

52-year-old Khalid Masood mowed down people injuring as many as 40 and stabbed a police officer to death as he tried to enter the U.K. Parliament.

The police reportedly want to know if Masood was encouraged or supported by any groups.

MI5 is trying to understand Masood's involvement and belief in Islamic State's violent ideology. With the investigation on, fresh details about his life have also emerged.

So far, the police believe he acted alone when he drove a hired car into civilians on Westminster Bridge before running into the grounds of parliament and stabbing a police officer to death.

It has also emerged that on the eve of the attack, he had checked into a Brighton hotel under his own name. The hotel manager said that Masood had been "laughing and joking".

Since the attack, the police have arrested 11 people on suspicion of preparing terrorist acts.

On Friday, they released eight without charge, having eliminated them from their inquiries, and one woman was released on Thursday on bail. The two in custody are a 58-year-old man and a man aged 27, both arrested on Thursday in Birmingham.

Meanwhile, seventeen people are still being treated for their injuries in five London hospitals. Two of those are in critical condition, according to the Metropolitan police, with one person's injuries considered life-threatening.

Following the attack, several world leaders came forward and showed solidarity with London.