"There is no direct cooperation … Sometimes they convey messages … But there is nothing technical. There is no dialogue. There is, let's say, information," Assad said.
He added that the communication was being carried out through third parties, including Iraq.
The Syrian president also dismissed allegations that his country's forces had been dropping barrel bombs on the territories held by rebel groups, killing thousands among the civilian population.
Syria is dealing with a civil war that broke out in 2011, with government forces clashing with armed rebel groups, including the Islamic State, which are fighting to overthrow the Assad regime.
To stop the advance of IS militants, the US-led coalition of more than 60 nations are carrying out airstrikes against the extremist group in Iraq and Syria. The coalition did not receive an approval from Damascus when it launched air raids on Syria's territory in September 2014.
