According to reports, a commander, who had led the militants in the countryside of the Syrian capital Damascus, was among those joining the Syrian government forces.
The defectors said they had been deceived into taking part in the foreign-sponsored militancy against the Syrian people and government.
According to the FSA militants, a large number of foreigners have joined the conflict in Syria during the past years.
They further disclosed that weapons supplied to foreign-backed militants wreaking havoc on Syria have been smuggled into the Arab country through Jordan while Saudi Arabia and Qatar paid for them.
The military coalition, which was established in 2011 to fight the Syrian government, has been weakened by the deep divisions among its members and its failure to make major gains.
Syria has been gripped by deadly violence since 2011.
The Western powers and their regional allies - especially Qatar, Saudi Arabia and Turkey - are reportedly supporting the militants operating inside Syria.
More than 191,000 people have been killed in over three years of fighting in the war-ravaged country, says the Office of the UN High Commissioner for Human Rights (OHCHR), calling the figure a probable “underestimate of the real total number of people killed.”