Pope Benedict XVI resigned after an internal investigation informed him about a web of blackmail, corruption and gay sex in the Vatican, Italian media reports say.

Three cardinals were asked by Benedict to verify allegations of financial impropriety, cronyism and corruption exposed in the so-called VatiLeaks affair.

Pope Benedict XVI around the time of his appointment.

On December 17, 2012, they handed the pontiff two red-leather bound volumes, almost 300 pages long, containing "an exact map of the mischief and the bad fish" inside the Holy See, La Repubblica said.

"It was on that day, with those papers on his desk, that Benedict XVI took the decision he had mulled over for so long," said the centre-left newspaper. It said its article was the first of a series.