Scotland Yard's top anti-terror officer says two more significant arrests have been made in connection with the Westminster attack.
Mark Rowley said nine people are now in custody in connection with the attack, and one woman has been released on bail.
Mr Rowley told a media conference there was no evidence of any further threat, but they were still trying to establish whether others directed the attacker, British-born Khalid Masood.
Masood, whose birth name was Adrian Russell, once came under the scrutiny of British intelligence services, but was not on any current watchlist.
A 75-year-old man died of his injuries in hospital today, bringing the death toll (including the attacker) to five.
The include police officer Keith Palmer, Aysha Frade and US tourist Kurt Cochran.
The 75-year-old man was receiving medical treatment in hospital, but his life support was turned off.
Mr Rowley said 50 people were wounded, two of whom remained in hospital in a critical condition.
In the attack, Masood drove a car into people on Westminster Bridge near the British parliament, before stabbing a police officer.
Masood was shot and died at the scene.
The so-called Islamic State group said it was behind the attack.