Moazzam Begg stands outside the U.S. Embassy in London, March 3, 2006. Alastair Grant/AP Photo

LONDON - A former Guantanamo Bay detainee who has written a book about his time in Gitmo and campaigned for the rights of terrorism suspects was arrested today on suspicion of attending a terrorist training camp and involvement in terrorism in Syria, British police told ABC News.

Moazzam Begg was arrested by specialist counter-terrorism police in the city of Birmingham, England, in an operation stemming from unspecified intelligence. Two other men and a woman were arrested in the operation and suspected of "facilitating terrorism overseas," according to police who say there was no immediate risk to public safety. None of the four have been charged. Their homes are being searched by police officers.

Begg, a British citizen, was arrested by the CIA in 2002 in Pakistan. He was initially held at Bagram, then transferred to Guantanamo Bay in 2004. Begg was released without charge in 2005. He has since written a book about his experience, in which he claims he was shackled and beaten, and has campaigned with a group that says it helps those who have been abused and mistreated in the global war on terror.

U.S. and British security officials have been warning for months about the threat posed by a surge in radicalized fighters returning home to Europe from the civil war in Syria. British intelligence services are increasingly monitoring their activities. Last month 16 people were arrested in the U.K. on suspicion of terrorism after traveling between Syria and the U.K., compared to only 24 during all of last year.