The United States has begun reconnaissance flights over Syria and is sharing intelligence about jihadist deployments with Damascus through Iraqi and Russian channels, sources told AFP on Tuesday.
"The cooperation has already begun and the United States is giving Damascus information via Baghdad and Moscow," one source close to the issue said on condition of anonymity.
The comments came a day after Foreign Minister Walid Muallem said Syria was willing to work with the international community against the jihadist Islamic State group, and US officials said they were poised to carry out surveillance flights over Syria.
The Syrian Observatory for Human Rights said foreign drones had been seen over the eastern province of Deir Ezzor on Monday.
"Non-Syrian spy planes carried out surveillance of Islamic State positions in Deir Ezzor province on Monday," the Britain-based monitoring group's director, Rami Abdel Rahman, said.
On Tuesday, Syrian warplanes bombed Islamic State positions in several areas of Deir Ezzor, an oil-rich province in the east of Syria, most of which is held by the jihadists.
A regional source told AFP that "a Western country has given the Syrian government lists of Islamic State targets on Syrian territory since just before air raids on Raqa, which started in mid-August."
The Islamic State, which emerged from Al-Qaeda's Iraq branch but has since broken with the worldwide network, controls large parts of Deir Ezzor and seized full control of Raqa province, further up the Euphrates Valley, on Sunday, with the capture of the army's last position, the Tabqa air base.
It has declared an Islamic "caliphate" in areas under its control in Syria and neighbouring Iraq, where US war planes have been targeting its positions since August 8.
US officials said Monday that Washington was ready to send spy planes into Syria to track the group's fighters but that the moves would not be coordinated with the government in Damascus.
Muallem warned Monday that any unilateral military action on its soil would be considered "aggression."