London: Police in London on Thursday said they had arrested a fifth British man on suspicion of Islamist-linked "terrorism" after saying earlier they had managed to avert a "significant plot".
The 20-year-old was arrested "on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism," the Metropolitan Police said in a statement.
The police said he was arrested on Tuesday along with the other four but this was not revealed "for operational reasons".
"A number of residential addresses and vehicles were searched by specialist officers in West and Central London as part of the investigation. These searches are now complete," it said.
The five are being held in central London police stations and the police have a warrant to hold them until October 14.
Of the other four, two are aged 20 and two aged 21. One of the 21-year-olds was tasered during his arrest, the police said.
British media named the man who was tasered as 21-year-old medical student Tarik Hassane and said he was arrested on a housing estate in the Ladbroke Grove area of west London.
Hassane is reported to have travelled to Syria.
The government estimates some 500 British men have joined the Islamic State group in Syria and Iraq.
Officials said 103 people have been arrested this year after returning from Syria and five of those convicted.
"These arrests and searches are part of an ongoing investigation into Islamist-related terrorism," the police said in a statement on Tuesday.
A Whitehall source said officers believe the raids were an "early disruption" of what could have been a "significant plot".
Metropolitan Police Commissioner Bernard Hogan-Howe described the operation as "quite serious".
A British Muslim human rights group meanwhile condemned the police tactics used in Hassane`s arrest and "alarmist media reporting" on the case.
CAGE said the raid had been "violent" and "excessive force" was used. "A door was broken down, stun grenades were thrown, and a taser used," the group said in a statement.