Pope Francis will meet the spiritual leader of the world's Sunni Muslims in an unprecedented encounter at the Vatican on Monday, the pontiff's spokesman said Thursday.

Sheikh Ahmed al-Tayeb, the grand imam of Cairo's Al-Azhar, the most prestigious institution in Sunni Islam, will have an audience with the leader of the world's 1.2 billion Catholics at St Peter's, Father Federico Lombardi told AFP.

"This audience is being prepared and has been scheduled for Monday," he said. "It will be a first."

The visit marks the restoration of cordial relations between the two faiths. Ties were soured under Pope Benedict XVI after Francis's now-retired predecessor made a September 2006 speech in which he was perceived to have described Islam as a violent religion.

Dialogue resumed in 2009 but was suspended again by Al-Azhar in 2011 when Benedict called for the protection of Christian minorities after a bomb attack on a church in Alexandria, an intervention that was perceived as meddling in Egypt's internal affairs.

Relations have steadily improved since Francis became pope in 2013 with inter-faith dialogue near the top of his agenda, something he underlined with a personal message to the Muslim world to mark the end of the first month of Ramadan of his pontificate.