(CNN) Pope Francis has broken with papal protocol by kneeling to kiss the feet of South Sudan leaders at the Vatican.

A video released by the Vatican shows an aide on Thursday assisting the 82-year-old Francis, who was breathing heavily, so he could kiss the feet of President Salva Kiir Mayardit. He then moved on to Vice Presidents-designate Riek Machar and Rebecca Nyandeng de Mabior.

Kiir and Machar were once rivals, with Kiir accusing Machar -- his former deputy -- of staging a 2013 coup. Years of civil war followed. In 2018, they signed a peace agreement in Ethiopia, and they are now attempting to form a stable government together.

"To you three, who have signed a peace agreement," the Pope said, "I ask you as a brother, remain in peace."

The South Sudanese politicians were staying at the Pope's Vatican residence for an unprecedented two-day spiritual retreat, the idea of Archbishop of Canterbury Justin Welby, the head of the Anglican Church.

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