LONDON - British police said on Friday they had disrupted an active terrorist plot with raids in London and southeastern England. One woman was shot and seriously injured in the swoop.

Police said six suspects were arrested on terrorism-related charges. The woman, who is in her 20s, was in serious but stable condition in a hospital, police said.

She was under police guard but had not been arrested because of her condition. Her name has not been released. Police said she was the subject of an ongoing investigation.

Police did not provide details of the plot or explain the circumstances of the shooting. In footage filmed by a witness, what sounds like several shots ring out as police surround the row house in Willesden in northwest London on Thursday evening.

The raids by counterterrorism officers marked an increase in police activity in the hours after a man was arrested on Thursday near Parliament and Downing Street while allegedly carrying large knives in a rucksack. The suspect, who has not been identified, had been under police surveillance.

Police said on Friday the raids in north London and southeastern England were not related to the earlier incident, which reminded many of the March 22 attack on Parliament and Westminster Bridge that claimed the lives of one police officer and four pedestrians.

Metropolitan Police Deputy Assistant Commissioner Neil Basu said the Willesden raid disrupted an "ongoing" plot, but did not elaborate.

Basu said that in both the Willesden and Parliament incidents, "we have contained the threat that they posed."

Britain's official threat level from international terrorism stands at the second-highest, "severe," meaning an attack is highly likely. Officials have warned of a potential uptick in attacks as some Britons who have joined Islamic State return home as that group loses territory in Syria and Iraq.

The raids on Thursday led to multiple arrests. A 20-year old woman and a 16-year-old boy were arrested at the address where the woman was shot, as was a 20-year-old man nearby. A man and a woman, both aged 28, were arrested when they returned to the house later.

A 43-year-old woman in Kent county, south of London, was also arrested.

Police said the suspects were being held on suspicion of preparation of terrorist acts. They were being questioned.