Sicilian mafia boss Matteo Messina Denaro, who was arrested in January after spending 30 years on the run, according to Italian media reports.
The 61-year-old was suffering from cancer at the time of his arrest.
As his condition worsened in recent weeks he was transferred to a hospital from the maximum-security prison in central Italy where he was initially held.
He was convicted of numerous crimes, including for his role in planning the 1992 murders of anti-mafia prosecutors Giovanni Falcone and Paolo Borsellino – crimes that shocked Italy and sparked a crackdown on the Sicilian mob.
He was also held responsible for bombings in Rome, Florence and Milan in 1993 that killed 10 people, as well as helping organise the kidnapping of Giuseppe Di Matteo, 12, to try to dissuade the boy’s father from giving evidence against the mafia.
The boy was held for two years, then murdered.
Dubbed by the Italian press as “the last Godfather”, Messina Denaro is not believed to have given any information to the police after he was seized outside a private health clinic in the Sicilian capital, Palermo, on 16 January.
According to medical records leaked to the Italian media, he underwent surgery for colon cancer in 2020 and 2022 under a false name.
A doctor at the Palermo clinic told La Repubblica newspaper that Messina Denaro’s health had worsened significantly in the months leading up to his capture.