A woman suffered minor injuries after a parcel bomb exploded at an office in central London.
Scotland Yard's anti-terrorism unit was investigating the "small explosion" at the offices of the Capita Group, a business out-sourcing company which runs London's congestion charge system among other services.
The female employee was taken to hospital by ambulance and police set up a cordon around the address in Victoria Street, less than a mile from the Houses of Parliament.
A Scotland Yard spokesman said it was too early to say who may have been behind the incident.
He said: "We can confirm there has been a small explosion at an office in Victoria Street but we are not prepared to discuss who may be responsible at this stage."
He added that a "small package" appeared to be the source of the explosion.
Police were called at around 9.40am to the building, which is just 200 yards from Scotland Yard. The Met Police's explosives unit was sent to the scene.
The office was located above a row of shops and cafes, including a sandwich store and shoe repair business.
The office worker is understood to have suffered injuries to her hands. All six floors of the office were evacuated.
One witness said a fire alarm had sounded before all employees were told to leave the building.
