Time magazine said on Tuesday it had talked by Skype with the fighter, identified as Khalid al-Hamad, who appeared in a video that sparked outrage and condemnation, including from the Syrian opposition.
Hamad claimed he was driven to the gruesome acts by footage on the dead soldier's cellphone, showing him "humiliating" a naked woman and her two daughters.
The magazine said Hamad described participating in another acts of mutilating regime forces, including militiamen known as shabiha. "I have another video clip... In the clip I am sawing another shabiha with a saw. The saw we use to cut trees. I sawed him in small pieces and large ones," Time quoted him as saying.
The magazine said Hamad, a Sunni like much of the opposition fighting against President Bashar al-Assad's regime, expressed hatred of member's of the leader's Alawite sect. "Hopefully we will slaughter all of them," he told the magazine,
"They were the ones who killed our children in Baba Amr and raped our women," he said, referring to a neighbourhood of the central city of Homs. "We didn't start it, they started it," he added. "Our slogan is an eye for an eye and a tooth for a tooth."
The video, in which Hamad leans over a uniformed body, cuts out organs and then holds one up to his mouth, has prompted both outrage and condemnation.
The National Coalition, the country's main political opposition grouping, issued a statement saying it "strongly condemns" the act. "The Coalition stresses that such an act contradicts the morals of the Syrian people, as well as the values and principles of the Free Syrian Army," it said.
"The Syrian Coalition reiterates its condemnation of such an act and stresses that it is a crime, regardless of the perpetrator. "The culprit will eventually be tried in court in front of an honest and fair judiciary." Human Rights Watch said condemnation alone was not sufficient.
"It is not enough for Syria's opposition to condemn such behaviour or blame it on violence by the government," said Nadim Houry, Middle East deputy director at the New York-based watchdog. "The opposition forces need to act firmly to stop such abuses."