Cardiff has an ongoing problem with the radicalisation of young Muslims, said an academic who has studied the issue.
Two men from the city have been identified taking part in what appears to be a Jihadist recruiting video, which was posted online last week.
It is thought Reyaad Khan travelled to Syria with friend Nasser Muthana who also appears in the footage.
Khan lived close to the Cardiff men jailed over the London Stock Exchange bombing plot in 2012.
It is believed the two men, both 20, travelled to Syria in November, while Nasser Muthana's younger brother Aseel, 17, travelled to the country in February.