Pope Francis on Saturday imposed mandatory term limits on one of his most powerful aides, the head of the powerful College of Cardinals, as he continues his wide-ranging institutional reform of the Vatican.

The pontiff announced that the college's dean would now be limited to two five-year terms - a change from current rules that allow the dean to remain in post as long as he chooses.

Francis made the change shortly after accepting the resignation of Cardinal Angelo Sodano, a 92-year-old conservative who has wielded huge power since taking over in 2005.

The pope has consistently sought to reshape the roles of senior Vatican officials and introduce oversight into adminsitrative processes - the latest move coming last week when he abolished secrecy rules in sexual abuse cases.

Copyright Agence France-Presse, 2019