Muslim preacher Anjem Choudary was among those held, media reports say.
British police arrested nine men as part of an operation into Islamist-related militancy on Thursday, with media reporting the country’s most high-profile radical Muslim preacher was among those held.
Britain last month raised its international threat level to the second-highest classification of “severe”, meaning an attack is considered highly likely, and Prime Minister David Cameron has said the Islamic State group battling for territory in Syria and Iraq poses the country’s greatest ever security risk.
Police said the arrests were not in response to any immediate threat but that the men were held on suspicion of encouraging terrorism and belonging to and supporting a banned organisation.
“These arrests and searches are part of an ongoing investigation into Islamist-related terrorism,” police said in a statement.
The BBC and Sky News reported that one of the men held was Anjem Choudary, the former head of the now banned organisation al-Muhajiroun. It gained notoriety for staging events to commemorate the September 11, 2001 attacks on the United States with leaflets that referred to the hijackers as “the Magnificent 19”.
Police declined to confirm if Mr. Choudary, who has recently spoken out against the West’s intervention against Islamic State, had been held or to give further details. There was no answer from his mobile phone when contacted by Reuters.
The men, aged between 22 and 51, were in custody at police stations in central London while 19 properties across the capital and in Stoke-on-Trent in central England were being searched.
Mr. Choudary’s followers have been linked to a number of militant plots in the past, and one of the men who hacked a British soldier to death on a London street in May 2013 had attended demonstrations the preacher had organised.
Mr. Choudary has never been charged with any terrorism-related crimes.
In 2011, his home and a community centre in east London where he used to teach were raided by counter-terrorism police. He told Reuters at the time that he had done nothing illegal.
“The definition of terrorism is more suitable for the US/UK policy in Muslim lands than those who are removing their oppressive regimes,” Mr. Choudary said in a tweet he wrote hours before the police arrests.
“The war being waged by the US/UK & co is a war against Islam & Muslims. The objective is to take Muslims away from the Shari’ah (Islamic law)”
Al-Muhajiroun’s Syrian-born founder Omar Bakri was banished from Britain in 2005.