Al-Azhar, the prestigious seat of Islamic learning that is based in Cairo but respected by Sunni Muslims across the world, has steadfastly condemned gruesome executions claimed by the Islamic State group.

The millennium-old institution has emerged as a leading theological centre of Sunni Islam, the main branch of the religion, and shows a will to promote moderate Islam and dialogue with Christians.

It was swift in denouncing the immolation of a Jordanian fighter pilot by IS, which claims to have established an Islamic caliphate and imposes an extreme version of Islamic law in territories it controls in Iraq and Syria.

The group, accused by the United Nations of carrying out ethnic cleansing and crimes against humanity, has regularly claimed to have carried out beheadings and kidnappings in Syria and Iraq.

In a video released Tuesday, IS showed its militants burning Jordanian pilot Maaz al-Kassasbeh alive in a metal cage.

Kassasbeh had been captured in Syria when his plane went down in December.

Al-Azhar's grand imam, Ahmed al-Tayib lashed out at the militants over his murder, expressing his "strong dismay at this cowardly act."

This "requires the punishment mentioned in the Koran for these corrupt oppressors who fight against God and his prophet: killing, crucifixion or chopping of the limbs," said Tayib.

"Islam forbids killing of the innocent human soul... It forbids mutilating the human soul by burning or in any other way even during wars against an enemy that attacks you."

Tayib's verbal assault on IS was not his first.

At an international conference against extremism organised by Al-Azhar in December, he condemned IS for its "barbaric crimes," which he said was an "attempt to export their false Islam."

He also called on the United States and its allies to fight IS, and the conference itself urged Christians in the Arab world to stand firm in the face of jihadist violence and not go into exile.

US Secretary of State John Kerry pointed out during a visit to Cairo the importance of Al-Azhar's role in the fight against the group.

Critics often accuse the Tayib-led Al-Azhar of holding a view of Islam that is close to the one adhered by the Egyptian government.

Officially it has kept its distance from the now blacklisted Muslim Brotherhood and Salafists, although within Al-Azhar there are some who follow their ideologies.

The institution supervises several universities across the country offering courses to thousands of Muslim students from around the world.

It was founded in 970 by the Shiite Fatimid dynasty that ruled Egypt between 969 and 1171, but was converted to Sunni Islam after a Sunni dynasty took over the country.

The name Al-Azhar means "The Most Radiant" and was adopted in honour of Fatima al-Zahra, daughter of the Muslim prophet Mohammed.