MOSCOW (Sputnik) — Matvienko told reporters:
"This is unacceptable, without an appropriate request from the Syrian authorities it will be another flagrant violation of international law."
On Tuesday, US Defense Secretary Ashton Carter said the Pentagon had not ruled out conducting attacks on the ground against ISIL terrorists.
According to Matvienko, the United States "has already flagrantly violated international law" by organizing an air operation in Syria without an approval from the UN Security Council or Damascus.
Since the beginning of the war, the United States and some of its allies have supported "the moderate" Syrian opposition and called for Assad's resignation, while Russia recognized Assad as the only legitimate Syrian authority.
On September 30, Russia began an anti-ISIL air campaign in Syria at Assad's request.