An audio recording, believed to come from Islamic State leader, Abu Bakr al-Baghdadi, was posted online on Saturday.
The audio features a man’s voice saying that the more intense the war against their “caliphate”, the purer it becomes and the tougher it gets.
The man also slammed Saudi Arabia’s efforts to set up a coalition of Muslim nations to fight his group.
The authenticity of the message has not been verified, but it appeared as the IS militant group comes under intensifying military pressure in recent weeks.
A U.S.-backed alliance of rebels in Syria said it captured a Syrian dam on Saturday from Islamic State, cutting a main supply route of the militants across the Euphrates.
In Iraq, government troops were pushing deeper into the heart of the last remaining district held by Islamic State in the city of Ramadi.
The last such online public message said to be from Baghdadi was posted in May. He has been reported injured or killed several times in fighting.