The head of Al-Azhar, one of the most prestigious centres of Sunni Islam learning, condemned Wednesday "barbaric crimes" committed by the Islamic State group in Iraq and Syria.

Militants are acting "under the guise of this holy religion and have given themselves the name 'Islamic State' in an attempt to export their false Islam," Sheikh Ahmed al-Tayeb told the opening session of a two-day international conference in Cairo on fighting extremism.

"I wonder and ask why this blind division exists that has tainted Arab blood," Sheikh Tayeb said, adding that religious, political and economic factors were behind the emergence of groups such as IS.

But "some feel that our suffering is also a plot by Israel so it remains the most powerful country in the region, and that possibility can not be excluded", he said.

Sheikh Tayeb called on the US-led coalition that is fighting IS "to confront those countries who support terrorism financially and militarily".

"But we should not ignore our own responsibility for the emergence of extremism that has led to the formation of organisations such as Al-Qaeda and other armed groups."

The United States launched its first air strikes against IS in Iraq in August. In late September, it extended the campaign to IS targets in Syria, joined by several Arab allies.

On Wednesday, the Pentagon said Iranian warplanes had also carried out air strikes against IS in Iraq, a claim Tehran refused to confirm or deny.

The Cairo conference, organised by Al-Azhar, is being attended by delegates from several countries including Saudi Arabia, Iran and Morocco.

Later Wednesday, Saudi spy chief Prince Khaled bin Bandar bin Abdul Aziz met Egyptian President Abdel Fattah al-Sisi, and the two "emphasised the pivotal role of Al-Azhar in correcting the mistaken understandings about Islam, and in fighting terrorism," Sisi's office said.

"The two discussed regional issues concerning Iraq, Syria and Yemen... and agreed that Arab and Islamic countries must share responsibilities in fighting terrorism through coordination and joint efforts".