"We think this delivery is a stabilizing factor and that such steps, in many ways, restrain some hotheads from exploring scenarios in which this conflict could be given an international character with participation of outside forces," Ryabkov said.
The United States and Israel have both urged Russia not to deliver the missile batteries to Syria, which would constitute an upgrade to Syria’s air defenses.
Russia has been one of Assad’s biggest international backers and has argued against foreign intervention in Syria's two-year civil war.
On Tuesday, Israeli Defense Minister Moshe Yaalon warned that Israel was prepared to strike any shipments of the S-300s from Russia, according to The Associated Press.
“As far as we are concerned, that is a threat,” Yaalon told reporters Tuesday when asked about the S-300s. “At this stage, I can’t say there is an escalation. The shipments have not been sent on their way yet. And I hope that they will not be sent,” he said. “If, God forbid, they do reach Syria, we will know what to do.”
The Russians vow to provide weapons to Assad comes as the European Union is allowing a Syrian arms embargo to expire at the end of the month, which would allow European countries to send weapons to the Syrian opposition.
Ryabkov said that the expiration of the E.U. ban was “essentially throwing fuel on the fire in Syria," according to Reuters.