Former Guantanamo Bay detainee Moazzam Begg was among four people arrested in Britain yesterday on suspicion of terror offences relating to Syria, police said.
Begg, 45, who is now a human rights activist, was detained on suspicion of attending a terrorist training camp and facilitating terrorism overseas, said West Midlands Police.
Begg was held in the Guantanamo Bay detention camp for nearly three years after being arrested in Pakistan in 2002.
The British citizen was released without charge in 2005 and has since become a speaker and activist for a prisoner rights organisation.
Yesterday, he was among four people arrested at their homes in Britain's second city of Birmingham, central England, "on suspicion of Syria-related terrorism offences".
A 44-year-old woman and her son aged 20 were held on suspicion of facilitating terror abroad, as was a 36-year-old man at a separate address.
"We can confirm that Moazzam Begg was arrested," a West Midlands Police spokeswoman said.
"This is an arrest, not a charge, and ... our naming does not imply any guilt."
The three homes were being searched by officers from the West Midlands Counter Terrorism Unit, while vehicles and electronic equipment were being removed for forensic analysis.
"All four arrests are connected," said Detective Superintendent Shaun Edwards, the unit's head of investigations. "They were pre-planned and intelligence-led."
The suspects were being held at a police station in the Birmingham area.
European countries face a growing number of young people going to fight in Syria, where a civil war is raging involving President Bashar al-Assad's forces, rebels and Islamist fighters.
Britain has seen a major increase in Syria-related arrests in recent months.
Begg is the first former Guantanamo detainee to be arrested in Britain in connection with Syria.
Birmingham-born Begg moved to Afghanistan with his wife and three children in 2001, where he insisted that he was involved in charitable activities. He moved to Pakistan after the US-led invasion of Afghanistan and was detained as an "enemy combatant" in Islamabad in 2002.