"Most of the rebels have some education; it was not hard for them to detect the American accent of the trainer. He spoke through a translator. But the way he spoke indicated that he was American," the commander told BBC on condition of anonymity.

He said the two-week-long training courses, which take place at a military facility outside the Jordanian capital, focus on small and medium arms, as well as mortars and rocket-propelled grenades.

Despite Amman’s denial, other militant leaders have also confirmed taking two-week-long training courses in relatively small groups on Jordanian soil.

Jordanian Salafi extremist leader Mohamed al-Shalabi, known as Abu Sayyaf, said in an interview that he is currently recruiting Jordanian youths to fight in Syria. After being sent to Syria, the young men join the terrorist al-Nusra Front.

Shalabi said at least 30 al-Qaeda-linked Salafis have so far been killed in Syria. The Salafi leader also said that he motivates his men by telling them that "it is the duty of every Muslim to help the defenseless people of Syria.’

The al-Nusra Front has formally pledged allegiance to al-Qaeda leader Ayman al-Zawahiri.

For the time being, the FSA and the al-Nusra Front have common objectives in Syria. However, Shalabi says his personal belief is that "more wars will be on the way after a regime change in Syria."

Meanwhile, an FSA commander says that secular foreign-backed militants in Syria will break away from different groups fighting against Syria and eventually join the al-Qaeda operatives for financial reasons. The commander added that the FSA’s financial problems have led many of its militants to join the al-Nusra Front. The al-Nusra Front is bankrolled by the governments of Qatar and Saudi Arabia.

The unrest in Syria began in March 2011, and many people, including large numbers of army and security personnel, have been killed in the violence.

Damascus says the West and its regional allies, including Qatar, Saudi Arabia and Turkey are supporting the armed groups.