DUBAI: Al-Qaeda's leader Ayman al-Zawahiri on Thursday pledged his group's allegiance to the new Taliban chief Mullah Akhtar Mansoor who is facing a bitter struggle over his leadership.

“As emir of Al-Qaeda, I pledge to you our allegiance, following the path of Sheikh (Osama) bin Laden and his martyred brothers in their allegiance to Mullah Omar,” Zawahiri said in a recording, referring to the former Al-Qaeda leader and to the longtime Taliban chief, whose death was confirmed last month.

Mansoor, a longtime trusted deputy of Omar, is taking charge as the movement faces growing internal divisions and is threatened by the rise of the self-styled Islamic State (IS) group, which is making inroads in Afghanistan.

Zawahiri's pledge comes as Al-Qaeda also faces a growing rivalry for preeminence in the global jihadist movement with IS, which has seized control of large parts of Syria and Iraq.

The recording was featured in a video that opens with images of bin Laden -- who was killed by US special forces in Pakistan in 2011 -- pledging allegiance to Omar.

The recording then plays over a picture of Zawahiri, who is believed to be in hiding in the Afghanistan-Pakistan border region.

He says that the “Islamic emirate” established by the Taliban in Afghanistan was the “first legitimate emirate after the fall of the Ottoman Empire, and there is no legitimate emirate in the world apart from it."

He pledged to Mansoor to “implement sharia law” and to continue “jihad until every part of occupied Muslim land is free."

Mansoor was announced as the new Taliban chief on July 31, after the movement confirmed the death of Omar, who led the Islamist insurgency for some 20 years.

'True to Islamic tradition'

But splits have emerged in the Taliban following the appointment, with some top leaders, including Omar's son and brother, refusing to pledge allegiance to Mansoor.

Taliban spokesman Zabihullah Mujahid acknowledged the news of Zawahiri's pledge of allegiance, but said that, “We will react about it later. We don't want to comment on it now.“

Pakistani analyst Imtiaz Gul, an expert on Al-Qaeda and the Taliban, added that Zawahiri's announcement is logical and true to the Islamic tradition of governance and succession, which is to say that whoever commands the majority of the Taliban should rightfully be the successor.

“This is in keeping with their political ideology. These organisations contest the idea of hereditary succession,” he added.

Just two days after the succession announcement, the late leader's son, Mullah Yakoub, and his brother, Mullah Abdul Manan, refused to pledge allegiance to Mansoor, calling on religious scholars to settle the rift.

Yakoub and several other members of the Taliban's ruling council walked out of the meeting at which Mansoor was declared leader, refusing to pledge loyalty to him, a Taliban source said.

But official Taliban statements in the name of Omar, who had not been seen in public since the Taliban were toppled from power in 2001, were released as recently as July.

Mullah Mansoor is one of the founders of the Taliban movement and is seen as a moderate, pro-peace, pro-talks leader.

However, he has faced powerful rivals within the Taliban who are strongly opposed to peace talks with the Afghan government, with some insurgents also unhappy at the thought he may have deceived them for more than a year about Omar's death.