Moazzam Begg speaks at an Amnesty International news conference in Berlin on Feb. 12, 2010. (Simon Klingert/AFP/Getty Images)

Former Guantanamo Bay detainee Moazzam Begg was among four people arrested in Britain on Tuesday on suspicion of terrorism offenses related to the war in Syria, British police said.

Begg, 45, was arrested at his home in south Birmingham on suspicion of “attending a terrorist training camp and facilitating terrorism overseas,” the West Midlands Police said in a statement.

Besides Begg, police arrested a 44-year-old woman, her 20-year-old son and a 36-year-old man on “suspicion of facilitating terrorism overseas.” Police said their homes, all in the area of Birmingham, Britain’s second-largest city, were being searched, along with their vehicles and electronic devices.

British authorities are increasingly concerned about the threat posed by Britons returning home after becoming radicalized in Syria. In 2013, British police made 24 arrests related to Syria; in the first three weeks of January 2014, they made 14.

In an unusual step, a West Midlands Police spokeswoman named Begg as one of the four arrested.

“We are confirming this name as a result of the anticipated high public interest,” she said, adding that “our naming does not imply any guilt.” The three others were not named.

Shaun Edwards, detective superintendent of the West Midlands Police counterterrorism unit, said the four arrests were connected. “They were pre-planned and intelligence-led,” he said in a statement.

Begg spent nearly three years in U.S. custody at prisons in Afghanistan and in Guantanamo Bay, Cuba, before being released in 2005 without charge. Begg, who was born in Britain to Pakistani Muslim parents, was arrested in Pakistan in 2002 on suspicion of being an al-Qaeda member and was turned over to U.S. authorities.

Since returning to Britain, Begg has become a well-known campaigner for the rights of detainees and their families. He is the director of outreach for Cage, a London-based advocacy group formerly called Cageprisoners, and frequently speaks out on Syria.

Writing on the group’s Web site in December, Begg detailed the two trips he made in 2012 to Syria, where he said he was investigating allegations of U.S. and British complicity in rendition and torture, and visiting refugees.

“I witnessed the squalid refugee camps, I visited the wounded — young and old, some of whom I buried, I saw the carnage of [President Bashar al-Assad’s] killing machine and I saw the beautiful young faces of children aged beyond their years,” he wrote.

He also said that officials from MI5, Britain’s domestic intelligence agency, reached out to him before his second trip to discuss his views on Syria, and that MI5 assured him that he would not be “hindered” in returning to Syria.

But British authorities later seized his passport over his Syria trips, he wrote.

British police have a maximum of 14 days to release or charge Begg.