International efforts to stop the fighting in Syria have failed to end the conflict, as rebel fighters and the Assad government battle on with no immediate victory in sight. The involvement of foreign militants in the Syrian conflict complicates the situation even more.
Conflict in Syria has entered its fourth year, and the United Nations estimates the fighting has left more than 100,000 people dead. While the Assad regime is trying to crush the rebellion, the rebel groups are fighting back with support from much of the Syrian population and also from external backing - including some foreign fighters who go to Syria to fight alongside the rebels.
These foreign fighters come from several different countries says Daniel Serwer, a scholar at the Middle East Institute and professor at Johns Hopkins School of Advanced International Studies.
"They are mainly from the Middle East. But there are some from Europe and even a few from the United States. And you have some influx from Pakistan that is in the news," he said "It is serious problem."
Even though these foreigners are fighting against the Assad regime that Washington heavily criticizes for its alleged human right violations, Serwer says these radicalized millitants are of great concern to the U.S. as well.
"It is clear that Syria, or parts of Syria, risk becoming a haven for extremists, and they will use that haven as a platform eventually to launch attacks against the United States," he said. This has happened with Yemen, this has happened with Pakistan, and this has happened with Afghanistan."
Experts also say a lot of Syrians are hesitant to join the anti-Assad forces because of the presence of foreign fighters among their ranks. Fragmentation among the rebel groups benefits the Assad regime, says Leila Hilal, an expert on Syria with Washington’s New America Foundation.
"The opposition that is fighting against the Assad regime is factionalized, is fragmented and increasingly so," she said. "We have something in the number of 5,000 different fighting brigades. So, without the unification of the opposition fighters, it is very hard to mount to a successful campaign."
Peace talks between the Assad regime and rebel forces have not produced any positive results. And Halal points out the crisis in Ukraine has further diminished hopes for a diplomatic solution of the crisis.
"The impact that the Crimea situation is having on Syria is that it is undermining the ability of Russia and the U.S. to work together toward a diplomatic solution for Syria," she said,
The crisis in Syria has now caused more than two-and-a-half million people to flee the country and become refugees. Experts stress that further delay in finding a diplomatic solution to the conflict will only aggravate the humanitarian crisis.