Seven people have been arrested in raids following London attack that left four dead, police have said.
Acting Deputy Commissioner and Head of Counter Terrorism Mark Rowley said hundreds of detectives have worked through the night, carrying out searches at six addresses.
Those who died were a woman in her 40s, a man in his 50s, police officer Keith Palmer and the attacker, he said.
Seven of the injured are still in hospital in a critical condition.
A further 29 had been treated in hospital, Mark Rowley added.
In the attack on March 22, a man drove a car along a pavement in Westminster knocking down pedestrians, leaving dozens injured.
He then stabbed a policeman and was shot dead by police in the grounds of Parliament.
In a statement made outside Scotland Yard, Mark Rowley said: “The inquiries in Birmingham, London and other parts of the country are continuing.
“It is still our belief – which continues to be borne out by our investigation – that this attacker acted alone and was inspired by international terrorism.
“To be explicit, at this stage we have no specific information about further threats to the public.”
Mark Rowley said he would not name the bridge victims yet, who were “a mix of nationalities”, and urged journalists not to publish the attacker’s name while searches were continuing.
He said Londoners should expect to see more police officers on the streets, after officers’ leave had been cancelled and duty hours extended.
It was initially thought that three members of the public had been killed on Westminster Bridge, but Mark Rowley referred to just two in his statement.