The Washington Post reported that a U.S Army veteran was charged with conspiracy for fighting with a Syrian rebel group linked to Al Qaeda.

"Eric Harroun, 30, known to Syrians as "the American," crossed into northern Syria in January and joined members of Jabhat al-Nusra to fight against the Syrian military, according to an FBI agent's affidavit in support of a criminal complaint filed by prosecutors in federal court in Alexandria", the newspaper reported.

Al Nusra Front, one of the most effective rebel forces, was designated a terrorist organization by the State Department in December.

"Concerns about such groups as Jabhat al-Nusra have been cited by the Obama administration as one of the reasons the U.S. government has declined to provide weapons to the Syrian opposition. Instead, the rebels depend on arms provided by other countries, particularly Qatar and Saudi Arabia", the paper reads.

Harroun, who served in the Army from 2000 to 2003 and was medically discharged after being injured in a car accident, was detained by FBI agents Wednesday after he arrived at Dulles International Airport on an international flight from an unidentified location.