Al-Qaeda leader Ayman al-Zawahiri has denounced what he said was a dishonest propaganda campaign by rival jihadi group the Islamic State against his organisation.

In an audio message released on Thursday, the 65-year-old Zawahiri complained that Abu Bakr Al-Baghdadi, the IS chief, had alleged that Al-Qaeda opposes sectarian attacks on Shiites and was prepared to work with Christian leaders.

"The liars insist upon their falsehood, to the extent that they claimed we do not denounce Shiites," Zawahiri said, according to the translation of the message, which was released by Al-Qaeda's media arm. 

Al-Qaeda, founded by the late Osama Bin Laden, was locked in a battle with the Islamic State, which sprang from its Iraqi faction, for the leadership of a global jihad.

Zawahiri, an Egyptian, denied he had said that Christians could be partners in the governance of a future Islamic caliphate, having only said that they could go about their affairs within it.

"What I have said is that they are partners in the land, such as agriculture, trade, and money, and we keep their privacy in it, in accordance with the laws of our Sharia," he said.

He insisted he had not called for Shiite Muslims to be spared, but had suggested focusing attacks on Shiite-led Iraqi forces and not on random atrocities against civilians.

"I had told them several times to stop explosions in markets, husseiniyats (places if worship) and mosques, and to concentrate on military, security and police forces and Shiite militiamen," he said.

The IS and Al Qaeda have both carried out hundreds of attacks on civilian targets, but some Al Qaeda members have called for less indiscriminate tactics.

Zawahiri also denied Al-Baghdadi's charge that Al Qaeda supported ousted Egyptian President Mohammed Morsi, an Islamist who attempted to rule through the ballot box.

The Al Qaeda leader, who took charge after Bin Laden was killed by US commandos in 2011, is thought to be somewhere in Pakistan's unruly border region hiding from a global manhunt.

He communicates with the group's remaining supporters through semi-regular video lectures, reiterating the need to target the US.

The audio message restated the urgency to "tell America, to other than Allah we do not kneel" but also argued for a dialogue on tactics with other jihadis. 

It was translated by US-based watchdog the SITE Intelligence Group.