Al Qaeda chief Ayman al-Zawahiri has pledged allegiance to new Afghan Taliban leader Haibatullah Akhundzada, whose predecessor was killed in a US drone strike.

The pledge came in a 14-minute audio and video message posted online, the US-based monitor SITE Intelligence Group said on Saturday.

"We pledge allegiance to you on jihad to liberate every inch of the lands of the Muslims that are invaded and stolen, from Kashgar to al-Andalus, from the Caucasus to Somalia and Central Africa, from Kashmir to Jerusalem, from the Philippines to Kabul, and from Bukhara and Samarkand," it quoted Zawahiri as saying.

The message included images of al Qaeda founder Osama bin Laden, who was killed by US special forces in Pakistan in 2011.

Akhundzada was named by the Afghan Taliban as their new leader last month in a swift power transition after officially confirming the death of Mullah Mansour in a US drone strike.

Akhundzada, formerly one of Mansour's deputies, faces the enormous challenge of unifying an increasingly fragmented militant movement.

The drone attack that killed Mansour, the first known American assault on a top Afghan Taliban leader on Pakistani soil, sent shockwaves through the insurgent movement which had seen a resurgence under Mansour.

He was killed just nine months after being formally appointed leader following a bitter power struggle upon confirmation of founder Mullah Omar's death.