Later, he and other Russian officials continued to call for creating a united front against terrorism.
Russia started its aerial campaign against terrorists in Syria in 2015 at the request of the Syrian president.
"This is a cosmetic campaign against IS [Daesh]," Assad said in an interview with the US-based Yahoo News online outlet published Friday.
Assad further asserted that Daesh began losing ground following Russia's involvement in September 2015.
"It started shrinking after the Russian intervention, not the American one," he was quoted as saying.
The US-led coalition of 68 nations is conducting airstrikes against the Daesh in Syria and Iraq. The strikes in Syria are not authorized by the government of President Bashar Assad or the UN Security Council.