Pope Francis has made the most significant appointment of his pontificate so far, appointing a veteran Vatican diplomat as his number two.

Archbishop Pietro Parolin becomes the pope's secretary of state, Vatican prime minister and chief aide - a role often called the "deputy pope".

The appointment ends the era of Cardinal Tarciscio Bertone.

He was widely blamed for failing to prevent ethical and financial scandals during the eight-year reign of former Pope Benedict, who resigned in February.

Italian Archbishop Parolin is one of the Vatican's diplomatic elite and had been the Holy See's representative in Venezuela.