"They are not aid workers or visiting relatives — they are people of real concern that they are getting involved in fighting or are supportive of it. They are potential terrorist suspects,” Rowley said, as quoted by the BBC.
Rowley added that the number of Britons joining extremist groups abroad continues to grow.
According to Rowley, many Britons have been inspired by insurgent groups in Syria and are planning to conduct terrorist attacks in the United Kingdom.
Part of Syria is controlled by the Islamic State (ISIL) insurgent group, which has reportedly recruited thousands of Westerners.
London-based International Center for the Study of Radicalization and Political Violence estimates that over 600 Britons are currently fighting alongside the ISIL in Syria and Iraq.
