Al-Qaeda leader Ayman al Zawahiri has pledged allegiance to the new Afghan Taliban chief in an audio message posted online.

The pledge to Mullah Akhtar Mansour was issued by Al-Qaeda's media arm Al Sahab and was Zawahiri's first message since September last year, the BBC reported on Thursday.

There had been speculation about whether Zawahiri was himself dead since the death of former Taliban head Mullah Omar was confirmed last month.

Zawahiri offered his condolences.

Al-Qaeda and Zawahiri considered Mullah Omar to be the leader of the global jihadist movement.

This was however contested by Al Qaeda's rival, the Islamic State militant group, which announced the establishment of a caliphate last year.