Posted March 24, 2017 20:27:03

British police say they have made two further significant arrests in the investigation into the attacks on Westminster Bridge and the Houses of Parliament in London.

Metropolitan Police counter-terrorism chief Mark Rowley said police had nine people in custody after Wednesday's attack which killed five people, including the assailant.

Police had earlier said the man behind the attack was British-born Muslim convert Khalid Masood and that they were trying to establish if others had directed him.

"Our investigation focuses on understanding his motivation, his operation and his associates," Mr Rowley said.

"Whilst there is still no evidence of further threats, you'll understand our determination is to find out if either he acted totally alone, inspired perhaps by terrorist propaganda, or if others have encouraged, supported or directed him."

Mr Rowley said police had made two further "significant" arrests overnight, one in the West Midlands and one in the north-west of the country.

"We now have nine people remaining in custody, and one woman has been released on bail," he said.

Masood had shown up on the periphery of previous terrorism investigations that brought him to the attention of Britain's MI5 spy agency.

But he was not under investigation when he sped across Westminster Bridge on Wednesday, ploughing down pedestrians with a hired car before running into the parliamentary grounds and fatally stabbing an unarmed policeman. He was shot dead by police.

Mr Rowley said at least 50 people were injured in the attack.

He named 75-year-old Lesley Rhodes as the fourth victim, who died in hospital on Thursday.

Two remain in hospital in a critical condition, one with life-threatening injuries.

Scotland Yard said they have seized close to 3,000 items in raids across the country, including what is thought to be critical computer data.

Reuters/ABC

Topics: terrorism, murder-and-manslaughter, crime, united-kingdom