Police secure the area close to the Houses of Parliament in London, Wednesday, March 22, 2017.

A woman was shot by police in London during an anti-terror raid on Thursday following an intelligence operation, the city’s Metropolitan Police said.

The woman in her twenties was shot at an address in north-west London during an “ongoing counter terrorism investigation”, police said in a statement. She was one of the subjects of the terror probe and remains under police guard in hospital.

The evening raid saw three people arrested on terrorism charges, including two at the scene – a 16-year-old boy and a 20-year-old woman – as well as a 20-year-old man nearby.

Police also arrested a 43-year-old woman in Kent, south-east England, following the London raid. “All four have been arrested on suspicion of the commission, preparation and instigation of terrorist acts,” police said.

Under observation

“The address and persons connected with it had been under observation by counter terrorism officers as part of an ongoing intelligence led operation.”

Police said the probe was unrelated to the arrest earlier on Thursday of a man armed with knives close to the Houses of Parliament. The 27-year-old was arrested on terrorism charges after being surrounded by firearms officers who pinned him to the ground.

The area around parliament has been on a state of heightened alert since a deadly attack on March 22 perpetrated by Khalid Masood. Masood drove into pedestrians, killing four, and stabbed a police officer to death at the gates of parliament before being shot dead by an armed officer.