A priest and another Christian were beheaded as a crowd of Syrian insurgents cheered.
A video shows the two unidentified men, with their hands tied, surrounded by a cheering crowd of dozens just moments before their heads were cut off with a small knife.
The attackers, who claimed the victims aided President Bashar al-Assad's military, then lifted a head for show and placed it back on one of the bodies.
The shocking images emerged as Syrian government forces launched a withering offensive against rebel-held parts of the central city of Homs, determined to deal the final blow to the "capital of the revolution".
The Syrian army, reportedly backed by the Lebanese militant group Hizbollah, has dramatically escalated an attack against rebel-held pockets of Homs, seeking to consolidate control of the area from Damascus to the Mediterranean coastline.
"The campaign started yesterday morning against the besieged neighbourhoods in Homs Old City," Abu Fidaa, an opposition activist speaking from inside the area said.
"In the first two hours we were attacked with more than 200 missiles. They are destroying everything. It is as if President Assad wants to burn the area," he added. (© Daily Telegraph, London)