Al-Qaeda's Iraqi front group claimed an attack on a convoy in west Iraq that killed 48 Syrian soldiers and nine Iraqi guards in a statement posted on jihadist forums on Monday.
The soldiers had entered Iraq for medical treatment and were being transported through the western province of Anbar on their way back to Syria when the attack took place on March 4, according to the Iraqi defence ministry.
Islamic State of Iraq fighters were able to destroy a column of "the Safavid army with its associated vehicles" carrying "members of the Nusairi army and Syrian regime 'shabiha'," the statement said.
Safavid is a word implying Shiites under Iranian control, while Nusairi is a derogatory term for Alawites, the sect to which Syrian President Bashar al-Assad belongs, and shabiha is a name used for pro-regime militia forces.
Baghdad has consistently avoided joining calls for the departure of Assad, whom rebels are battling to overthrow, instead saying it opposes arming either side and urging an end to the violence that has ravaged Syria for the past two years, leaving at least 70,000 people dead.
But the deadly ambush in its territory threatens to entangle Iraq in the conflict.
Baghdad is caught between conflicting pressures over Syria - its powerful eastern neighbour, Shiite Iran, backs Assad, while the United States and many Arab states want Assad to bow to opposition demands and step down.