British former Guantanamo Bay detainee Moazzam Begg is among the four people who have been arrested in the UK on suspicion of Syria-related terrorism offences.
Begg, 45, from Birmingham, who was held in the US-run military prison in Cuba for nearly three years, is suspected of attending a terrorist training camp and facilitating terrorism overseas, West Midlands Police said.
A 36-year-old man and a 44-year-old woman and her 20-year-old son, also from Birmingham, in Birmingham, have also been arrested on suspicion of facilitating terrorism overseas.
All four are being held at a police station in the West Midlands, police said, while their three home addresses are being searched by officers from the West Midlands Counter Terrorism Unit. Vehicles and electronic equipment are being removed for forensic analysis.
"We can confirm that Moazzam Begg was arrested this morning," a West Midlands Police spokeswoman said.
"We are confirming this name as a result of the anticipated high public interest to accredited media."
She added naming Begg does "not imply any guilt".
Head of investigations for West Midlands Counter Terrorism Unit, Detective Superintendent Shaun Edwards, said: "All four arrests are connected. They were pre-planned and intelligence led. There was no immediate risk to public safety."