Pope Francis has washed the feet of a dozen inmates at a juvenile detention centre in a Holy Thursday ritual that he celebrated for years as archbishop and is continuing now that he is Pope.

The Mass was held in the Casal del Marmo facility in Rome, where 46 young men and women currently are detained.

Many of them are gypsies or North African migrants, and the Vatican said the 12 selected for the rite were not necessarily Catholic. In a break from tradition, two were women.

Because the inmates are minors, the Vatican and Italian Justice Ministry limited media access inside.

But Vatican Radio reported that Pope Francis told the detainees that Jesus washed the feet of his disciples in a gesture of service.

He said: "If the Lord has washed his disciples' feet, you should do the same."