Confident of victory: IS leader Abu Bakr al-Baghdadi on Mosul offensive

Islamic State's (IS) media arm has released an audio purportedly featuring its leader, Abu Bakr al-Baghdadi, in which he says he's "confident of victory" in Mosul, the group's Iraqi stronghold.

Addressing the estimated 5,000 fighters holed up in the city, he said that "holding your ground in honour is a thousand times better than retreating in disgrace," CNN reported on Thursday.

The tape was released by IS' media wing al-Furqan as the battle for Mosul intensifies, with Iraqi troops poised to enter the city.

It is the first recording reportedly of al-Baghdadi released since late 2015.

The sectarian tone and animosity toward Shia Muslims and other, non-Muslim groups is more vicious than in previous recordings.

The voice, which CNN cannot independently verify, says that "God's enemies from the Jews, Christians, atheists, Shiites, apostates and all of the world's infidels have dedicated their media, money, army and munitions to fight Muslims and jihadis in the State of Nineveh after they witnessed it become one of the bases of Islam and one of its minarets under the Caliphate," he said.

Ninevah is an archaic name for the modern day Mosul region.

The audio, which is nearly 32 minutes long, references Turkey's massing of armaments along the Iraq-Turkey border, suggesting that the recording was made very recently.

Along with rallying IS-affiliated fighters across the globe, he warns jihadis against "conflict and disagreement".

"You need to be one and united in your fight against your enemy. You should seek to raise the word of God on Earth," he said.

The leader of the brutal Islamist group first came into the public eye with a sermon delivered at the Great Mosque of al-Nuri in Mosul in July 2014.

The most recent audio message attributed to al-Baghdadi surfaced online in December 2015, mocking the Western coalition aligned against him, threatening Israel and trying to boost his own forces' morale.