Illustration: Syrian rebels in Aleppo
Illustration: Syrian rebels in AleppoReuters

US Intelligence officials estimate that at least 50 US citizens are fighting in Syria against President Bashar Assad, and are liable to bring terrorism back to the US once the war is over, according to the Los Angeles Times.

James Clapper, the US director of national intelligence, told the House Intelligence Committee Tuesday that as many as 7,500 foreign nationals are fighting in Syria from 50 countries. The estimate is much lower than reports from Syrian sources, who claim that the number is at least ten times that much - reaching over 75,000. 

An official told the Times that the number of Americans estimated to be fighting in the war is about 50, the first concrete estimate given by a US authority, according to the daily. Earlier estimates provided a wide range - between 10 and 60. 

Clapper expressed concern about the threat the US fighters could pose once they return, citing evidence that Al Qaeda has been training foreign nationals to bring the Islamic holy war outside of the Middle East. 

“Not only are fighters being drawn to Syria, but so are technologies and techniques that pose particular problems to our defenses,” Clapper said. FBI Director James B. Comey added that counter-terrorism experts are trying to locate and track US nationals involved in the fighting who have already returned home. 

This is not the first time that concerns have been raised about the presence of western-born and raised Al Qaeda fighters in Syria, including on the front lines of key battles.

In July, a US passport was found in an abandoned base that served the Islamic State of Iraq and the Levant (ISIS) organization, after Kurdish fighters pushed back Islamist forces in northern Syria following fierce clashes.

More recently, the Times notes, US citizen and Army veteran Eric Harroun, a Phoenix native, was charged with being involved with the Al Qaeda satellite the Al Nusra Front; Nicole Lynn Mansfield, a convert to Islam from Flint, Michigan, was killed after she joined a rebel faction in May. 

While Western countries - especially the US and Britain - have backed the rebel forces during the three year conflict, western states have become uneasy over the growing influence of radical Islamist elements among the rebel movement.

Recently, funding for some extremist rebel groups has been revoked, but foreign nationals - including many western citizens - continue to pour into Syria, and western security services are concerned about what this means for their own countries' future security. 

The Western countries have become so concerned, in fact, that they have reached out to Assad's regime forces over the issue - but no progress has yet been made.