Police said they had arrested four UK nationals from the Birmingham area on Tuesday on suspected terrorism offences related to Syria.
One, a 45-year-old man, is suspected of attending a terrorist training camp and facilitating terrorism overseas, West Midlands police said in a statement.
The other three, a 36-year-old man from Shirley, a 44-year-old woman and her 20-year old son from Sparkhill, were detained on suspicion of facilitating terrorism overseas. "All four arrests are connected. They were pre-planned and intelligence-led," said the head of investigations for West Midlands Counter-Terrorism Unit, Detective Superintendent Shaun Edwards.
The four were arrested at their homes.
Concern has been mounting in Britain over the number of UK nationals travelling to Syria to help rebels fighting President Bashar al-Assad. Police fear they may become radicalised by Islamists or attend terrorist training camps before returning to the UK where they could pose a security risk.
British police have already arrested 16 people on suspicion of terrorism offences related to Syria this year, some as young as 17, compared to 24 such arrests in all of 2013.