In his first message since U.S.-led Iraqi forces began their offensive to liberate Mosul city from the Islamic State group, also called ISIS, the terrorist group’s leader Abu Bakr al-Baghdadi purportedly expressed confidence in his fighters emerging victorious while urging them to attack neighboring Turkey.

An undated audio recording with a voice claiming to be that of Baghdadi’s was released early Thursday by the ISIS-affiliated media agency Al-Furqan. This is his first message since December 2015.

In the unverified recording shared by followers, Baghdadi told ISIS fighters to “unleash the fire of their anger” on Turkish soldiers who are waging war against the group in Syria and urged them to take the battle to Turkey.

“Turkey today entered your range of action and the aim of your jihad ... invade it and turn its safety into fear,” the reclusive leader reportedly said.

Of the Mosul offensive, Baghdadi said: “This ... total war and the great jihad that the Islamic State is fighting today only increases our firm belief, God willing, and our conviction that all this is a prelude to victory.”

“Do not retreat ... Holding your ground with honor is a thousand times easier than retreating in shame,” he added. The recording does not refer to Mosul, Iraq’s second-largest city, directly but the leader mentioned Nineveh, the province of which Mosul is the capital.

“To all the people of Nineveh, especially the fighters, beware of any weakness in facing your enemy,” Baghdadi reportedly said.

Baghdadi, whose whereabouts are unclear, also called for “attack after attack” in Saudi Arabia targeting government leaders, members of the ruling al-Saud family and Saudi media for “siding with the infidel nations in the war on Islam and the Sunna [Sunni Muslims] in Iraq and Syria.”

Iraqi forces backed by a U.S.-led coalition launched the offensive to liberate Mosul last month estimating that about 3,000 to 5,000 ISIS fighters are in the city. This is one of the most complex military operations Iraq has undertaken and it could spell doom for the militant group if Iraq is successful. ISIS has already lost dozens of villages and towns surrounding Mosul in just two weeks.