The cause of death was not reported.
Andreotti had been in ill health in recent years, ANSA said.
Andreotti was a politician of the defunct centrist Christian Democracy party. Besides becoming Italy's 41st prime minister in 1972, he was minister of the interior, defense and foreign office. He also was a senator for life since 1991.
His terms as prime minister were in the 1970s and from 1989 to 1992.
The Christian Democracy party dominated Italian politics after World World II until a series of corruption scandals led to its collapse in the early 1990s.
ANSA said Andreotti had been linked to shadowy events in Sicily for years.
In the late 1990s and early 2000s, Andreotti faced a series of trials involving Mafia ties, including the killings of one of his followers and of an investigative journalist. Andreotti was convicted and sentenced to 24 years in prison in 2002 for conspiracy to murder the journalist, but the verdict was overturned.
Investigative reporter Carmine Pecorelli, 51, editor of the weekly newspaper Osservatore Politico, was shot in the head and back four times as he left his Rome office on March 20, 1979. He had been planning to publish damaging revelations about Andreotti concerning matters connected to the 1978 kidnapping of Christian Democracy leader Aldo Moro and the collapse of an oil company, among other things, ANSA said.
ANSA said Andreotti wouldn't have served any prison time because of his age and because he was a senator for life, meaning he had immunity.
Asked once what he thought about the long sentence for the Pecorelli murder, Andreotti said it was a "good omen" for long life.