Syrian opposition activists say that the military has used chemical weapons against the Al Yarmouk district of Damascus, an area of the city comprised predominantly of Palestinian refugees, Israel Radio reported.
Palestinian sources said that 22 people have been killed in the area, most from inhalation of poisonous gases.
In what was considered a significant tactical and moral victory, forces battling to overthrow Syrian President Bashar Assad captured the Yarmouk region this past December.
The Syrian conflict has split Sunni loyalties, with Hezbollah following its patron Iran in backing Assad. Last year, the leadership of the Palestinian Islamic Jihad had left Syria for Iran but still remained on good terms with the Assad regime.
However, Palestinian Sunni terror group Hamas closed its offices in Damascus earlier this year, announcing in February that they were turning against the Alawite Assad and instead supporting the Sunni rebels.
In October, Syrian rebels announced they had begun arming sympathetic Palestinians, who would form a group called the Liwa al-Asifa (Storm Brigade) to fight against the PFLP-GC and take its Yarmouk stronghold.
The Popular Front for the Liberation of Palestine - General Command has accused the Liwa al-Asifa of trying to stir up trouble within the Palestinian refugee community in Yarmouk, while Syrian rebels have accused the PFLP-GC of stifling Palestinian dissent against Assad.
Last year, Liwa al-Asifa fighters had critically injured a senior PFLP-GC leader and killed four others in a car bombing attack in Yarmouk.