Six people have now been released out of the seven arrested over the 15 Sept attack at Parsons Green station in West London
British police said on Tuesday they had released three men who were arrested in connection with the bomb attack on a London underground train earlier this month.
Six people have now been released out of the seven arrested during the investigation into the 15 Sept attack at Parsons Green station in West London, London's Metropolitan Police said in a statement.
The one person who remains in custody is 18-year-old Ahmed Hassan, arrested in Dover, Kent, a day after the incident.
Hassan appeared in court on Friday charged with attempting to murder passengers on board the train heading to central London from the southwest suburb of Wimbledon.
He was also charged with causing an explosion likely to endanger life using the highly volatile triacetone triperoxide (TATP) - known as "the mother of Satan" - or another explosive substance.
The attack, using a home-made bomb that apparently failed to fully explode, was Britain's fifth major security incident this year and injured 29 people on a packed rush-hour commuter train.
The Islamic State militant group, which had said it was behind several attacks on Western cities in recent years, including two attacks in London and one in Manchester this year, claimed responsibility for the latest attack.