Unidentified gunmen assassinated Mohammad Maher Al-Rifai, a former officer in the Syrian Army who allegedly joined the opposition, in the country's southern province of Daraa.
"Rifai has defected the Syrian forces since the beginning of the revolution in 2011 and joined the opposition's Free Syrian Army," local media quoted sources as saying.
The sources pointed out that Al-Rifai, known as "Abu Bahr", had re-joined the regime's compulsory military service after a settlement agreement between Bashar Al-Assad's army and the opposition forces. They added that he had later joined the opposition again.
The local sources noted that the ex-soldier's family blamed the Syrian military's security branch for his assassination.
Syria has been ravaged by a civil war since early 2011 when the Assad regime cracked down on pro-democracy protesters.
Hundreds of thousands of people have been killed and more than ten million displaced, according to UN estimates.