Western governments and intelligence agencies have long voiced their concerns that the steady stream of young Muslims leaving their countries to fight in Syria are both fueling the conflict there and pose a potential security threat should they return home some day - radicalized and well-trained in military combat.
But despite efforts to stem the tide, Islamists from across Europe, North America and elsewhere in the western world are still managing to make their way to the battlefield, and continue to urge their coreligionists to join them
In a video released just today, an offshoot of Al Qaeda in Syria, the Islamic State of Iraq and the Levant (better known as ISIS) released a video hailing the successful arrival of three new British recruits.
In the clip, a British-born ISIS spokesman introduces one of the recruits, who goes on to encourage other Muslims to join him - and threatening Divine punishment for those who do not. The new arrival insists that despite measures by governments to prevent them, those who "put their faith in Allah" will find a way to join the jihad in Syria.
Though he did not elaborate on specifics, a recent documentary revealed how a well-known Islamist preacher in the UK was actively helping to vet recruits to join the ranks of Al Qaeda-linked rebels in Syria, as part of a wider network encouraging Muslims to answer he call to "holy war".
And it is not just men who are taking up the call - several Muslim women have also made their way to Syria, either as fighters or, in most cases, as wives for male fighters there.