"The actions they carried out go against international rights, for they have not been recognized by the UN General Assembly nor authorized by the Security Council," the Foreign Ministry said in a statement.
It added that Damascus' lack of consent makes the offensive a "violation of the state of Syria's sovereignty and a threat to its territorial integrity."
The statement came after US President Barack Obama spoke before the UN General Assembly, calling for a global effort to dismantle the jihadist "network of death."
France has also taken part in the offensive in Iraq.
"It is imperative that any military action get proper approval from the international community. Recent history teaches us that measures that are unilateral, as well as unlawful, exacerbate instability in those territories," the Ecuadoran government said.