Cairo: Al Qaeda leader Ayman Al Zawahri, in an online audio message, pledged allegiance to the new head of the Afghan Taliban, who was appointed last month after his predecessor was killed in a US drone strike.
The veteran extremist militant became Al Qaeda's leader after US Navy Seals killed Osama bin Laden in Pakistan in 2011, and he is thought to be hiding in the Pakistan-Afghanistan border region, having been based there since the late 1990s.
The authenticity of the recording could not be immediately verified.
Haibatullah Akhundzada, Islamic legal scholar who was one of former leader Mullah Akhtar Mansour's deputies, was appointed a few days after Mansour was killed by a US drone attack in a remote border area just inside Pakistan.
Since Al Zawahri, an Egyptian doctor-turned-militant, succeeded bin Laden, Al Qaeda has lost ground to IS in the leadership of the global extremist movement.
Some Afghan insurgent commanders have broken away from the Taliban to pledge support for IS, though it operates largely in Iraq and Syria, and is active in parts of North Africa.