Moazzam Begg was incarcerated for three years
Former Guantanamo Bay detainee Moazzam Begg is among four people who have been arrested on suspicion of Syria-related terrorism offences, police have said.
Mr Begg, 45, who was held by the US authorities for almost three years, was arrested earlier with two other men and a woman in the West Midlands.
He was detained on suspicion of attending a terrorist training camp and facilitating terrorism overseas.
West Midlands police said naming Mr Begg did "not imply any guilt".
A spokeswoman added: "We can confirm that Moazzam Begg was arrested this morning. We are confirming this name as a result of the anticipated high public interest."
The other people arrested - a 36-year-old man from Shirley, a 44-year-old woman and her son, 20, both from Sparkhill - are being held on suspicion of facilitating terrorism overseas.
Mr Begg, a British citizen originally from Birmingham, moved to Afghanistan with his family in 2001 before moving to Pakistan in 2002 when the war started.
He was arrested in Islamabad that January and taken to Bagram internment centre in Afghanistan for about a year before being transferred to the Guantanamo Bay US detention camp in Cuba.
He was released in January 2005 with three other British citizens and returned to the UK. He has always denied any involvement in any kind of terrorist activity.
BBC home affairs correspondent June Kelly said in recent years Mr Begg had been involved in an organisation called Cage, which helps families of people who have been detained.
She also said that in recent weeks there had been a big increase in the number of people being held by police in operations related to Syria.
Police say all four people arrested on Tuesday morning are being held at a police station in the West Midlands. Det Supt Shaun Edwards said the four arrests were connected.
He said: "They were pre-planned and intelligence-led. There was no immediate risk to public safety."
Counter-terrorism are searching their three homes and vehicles and electronic equipment have been taken away for forensic analysis, West Midlands Police said.