Lt. Gen. Alexander Lapin told reporters on Tuesday at Hemeimeem air base near the Syrian coastal city of Latakia that Syrian government forces have yet to clear the remaining 15 percent, approximately 27,000 square kilometers (10,425 square miles) from the extremists.

Russia has been providing air cover for President Bashar Assad's offensive against ISIS militants since 2015 and the support has changed the tide of the war.

Syrian troops have in recent weeks pushed out ISIS militants from the central Homs province, near the border with Lebanon, and are now fighting them in the oil-rich Deir el-Zour province in the east.