Defence Minister Antonio Martino has identified the latest victim as Pietro Petrucci, a 22-year-old volunteer from Naples.
His death brings to 19 the number of Italians killed in the attack, which also left eight Iraqis dead.
Earlier on Saturday Italian RAI2 television had quoted sources as saying the young man's family had agreed his life support machine should be turned off.
Petrucci had been in a coma since Wednesday's attack on the Italian police post in Nasiriyah. He had been in hospital in Iraq.
Martino could not say when Petrucci's body would be repatriated to Italy.
A military plane was due to arrive in Rome on Saturday evening with the bodies of the 18 other Italians killed in the attack.