Group claims man speaking in recording is its leader Abu Bakr al-Baghdadi, following reports he was wounded or killed.
Iraq’s prime minister has dismissed several top military commanders in a move seen as his boldest since he came to office in September.
Haider al-Abadi’s decision, aimed at boosting the morale of an army battling armed groups, came following a probe into claims of corruption, prompted by military defeats that enabled fighters of the Islamic State in Iraq and Levant (ISIL) to seize large expanses of the country.
Al Jazeera’s Imran Khan, reporting from Baghdad, said that 36 high-level officers in total were affected by the move: 26 were being reassigned and 10 forced to retire.
A senior officer at the country’s Defence Ministry told al-Jazeera that Abadi “wanted to send a message to the troops on the frontline that they were fighting for Iraqi unity, and that this was a signal fot the end of any sectarian values within Iraq’s armed forces”.
The officer asked not to be named as he was not authorised to talk to the media.
Iraq, which has been struggling for over a decade with violence and deep sectarian strife, has been facing near-daily explosions as well as an armed group that has captured a third of the oil-rich country.
Many analysts say the security and sectarian problems were compounded by former premier Nouri al-Maliki, who was accused by the country’s Sunni minority of favouring Shias and facilitating ISIL’s territorial gains as it faced weak resistance from Sunni tribes.
“It’s a a big morale boost for all the troops.,” Al Jazeera’s Khan said.
“They see their prime minister is serious about making changes, about handling allegations of corruption and about dealing with misconduct.”
Government forces, backed by air strikes carred out by a US-led coalition, are fighting against ISIL which has captured a third of the country.
In the northern city of Beiji, the army and backed by Shia fighters are jointly battling the Sunni armed group after they succeeded in pushing the group’s fighters out of the town centre.
The removal of those commanders, whose names have not yet been announced, was broadly welcomed across the political spectrum, as well as the Defence Ministry.
Hamed al-Mutlaq, a Sunni politician, said that “making these changes is positive and will in turn give more strength to the security apparatus, because a change is needed every now and then. There is a need for fresh blood”.