Although it has lost land in both Syria and Iraq, ISIS still holds large parts of the two countries of Iraq and Syria where as many 10 million people live under their control, according to Daily Mail.

Osama bin Laden's successor, al-Zawahiri, announced the plan in a speech posted online.

There have been reports that Al-Qaeda commanders have been sent to north-west Syria to begin their operation.

Saif al-Adel, a veteran Egyptian terrorist, seen as his deputy and operational field commander, is one of the men who has been sent.

The Jabhat al-Nusra (Nusra Front) terror group, which is allied to Al-Qaeda, would be responsible for the plan to take territory in Syria.

ISIS leader Abu Bakr al-Baghdadi set up the group but it split from him in 2013. It is known for being particularly brutal.

The US and its allies are concerned it could use Syria to launch attacks on the West like bin Laden did in Afghanistan.

Al-Qaeda has been concerned Jabhat al-Nusra could be persuaded by Persian Gulf states like Qatar to sever ties with them and disband in return for aid.

Zawahiri said he was 'proud' of Jabhat al-Nusra (Nusra Front) and its link to al-Qaeda in the video.

According to the Daily Telegraph, he said: 'If they create their government, and choose their emir, what they choose is our choice.'

He criticised ISIS and compared them to a centuries old Islamic group, Khawarij, which was brutal against fellow Muslims.

'The Islamic nation in Greater Syria has backed [al-Nusra], realizing the difference between the correctness of its methods and the methods of the new Khawarij,' he said.

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