A 25-year-old man has been arrested in Newport, Wales, in connection with the Parsons Green terror attack, Scotland Yard said.
The Met Police’s counter-terror police made the arrest at 7:08pm on Tuesday and a search of the property in south Wales continues.
Two other men arrested on Saturday remain in police custody.
Warrants for their further detention were granted by Westminster Magistrates’ Court.
Searches at two addresses in Surrey and a business in Hounslow, are still ongoing and are expected to last some days.
Commander Dean Haydon, head of the Met Counter Terrorism Command, said:
“This continues to be a fast-moving investigation. A significant amount of activity has taken place since the attack on Friday. We now have three men in custody and searches are continuing at four addresses. Detectives are carrying out extensive inquiries to determine the full facts behind the attack.
“We anticipate that the searches will take some days to complete and may cause further disruption. However it is important that we continue with these searches and I’d like to thank all those affected for their support, patience and cooperation.”
“As police and our partners do all we can to confront the threat, public vigilance remains as vital as ever.
“We urge the public report any suspicious activity to the police by calling us, in confidence, on 0800 789 321, or in an emergency by dialling 999.
“We are asking the public to look out for anything that seems out of place, unusual or just doesn’t seem to fit in with day-to-day life. It may be nothing, but if you see or hear anything that could be terrorist-related trust your instincts, then ACT, and call us.”
An improvised explosive device partially exploded on a District Line train at Parsons Green on Friday.
Some 30 people were injured in the incident, which took place at rush hour.