Prosecutors and judges have arrived at Italy's presidential palace for an unprecedented hearing to take testimony from the head of state in the trial of a former government official accused of negotiating with Mafia bosses to end terror bombings in the 1990s.

Prosecutors want to question President Giorgio Napolitano about communications he had with a now-deceased aide whose dealings with the main suspect, former Interior Minister Nicola Mancino, are being investigated.

Mancino is on trial for allegedly negotiating with the Mafia following the 1993 bombings of churches in Rome, the Uffizi museum in Florence, and a Milan park. Mancino has denied any negotiations.

Napolitano has said he had nothing useful to tell the court. But he agreed to testify.

The hearing occurred behind closed doors with no media present.