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 Islamist militant became al Qaeda’s leader after U.S. 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.

“As leader of the al Qaeda organisation for jihad, I extend my pledge of allegiance once again, the approach of Osama to invite the Muslim nation to support the Islamic Emirate,” al-Zawahri said in a 14 minute recording.

During its years in power, from 1996 to 2001, the Taliban established the Islamic Emirate of Afghanistan, and it has been fighting an insurgency since to regain control of the country.

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 U.S. 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 Islamic State in the leadership of the global jihadist movement.

Some Afghan insurgent commanders have broken away from the Taliban to pledge support for Islamic State, though it operates largely in Iraq and Syria, and is active in parts of North Africa.

Al Qaeda was set up by Arab guerrillas who flocked to Afghanistan to fight Soviet occupation forces in the 1980s. It had thrived under the Taliban’s rule before both groups were driven underground following the U.S. invasion that followed Al Qaeda’s Sept. 11, 2001 attacks on New York and Washington.

Ayman al-Zawahri Issues a Stark Warning Showing Real Tensions on the Ground

Al Qaeda leader Ayman al-Zawahri urged rival jihadist fighters in Syria to unite or risk death but again decried fellow Sunni Muslim militants Islamic State as “extremists” in an audio recording posted online on Sunday.

As successor to Osama bin Laden, Zawahri has the allegiance of al Qaeda branches in the Middle East, North Africa and South Asia. But the group’s dominance is being challenged by Islamic State, which controls territory in Syria and Iraq and  followings in Libya and Yemen.

In Syria, al Qaeda offshoot Nusra Front and Islamic State are the two most powerful groups fighting government forces. Once a single group, they split in 2013, largely due to a power struggle among leaders.

“We have to want the unity of the Mujahideen in Sham (Syria) so it will be liberated from the Russians and Western crusaders. My brothers … the matter of unity is a matter of life or death for you,” Zawahri said.

The authenticity of the recording, the first since January, could not be immediately verified, but it had the hallmarks of previous Zawahri tapes. In January, the Egyptian former doctor called for revenge after Saudi Arabia executed dozens of militants.

He is believed to be hiding in a border area between Afghanistan and Pakistan.

On the recording, Zawahri lambasted a U.N.-backed political process to find a solution in Syria, and praised Nusra Front, which controls most of Idlib province.

Nusra is also part of an alliance of Islamist brigades known as Jaish al Fateh, which is leading battles against Syrian government forces and its Russian- and Iranian-backed allies in the southern Aleppo countryside.

In January, Nusra Front tried unsuccessfully to convince rival Islamist factions to merge into one unit, including the powerful Ahrar al-Sham.

Zawahri also emphasised once again the ideological divide between al Qaeda and Islamic State, which is fighting a Western-led coalition and Russian forces while also clashing with Western-backed rebels and the Syrian army.

He described them as “extremists and renegades” whose followers would eventually disavow their beliefs and methods.