A spokesman for the Italian forces says the bomb was detonated by remote control.
Four other Italian soldiers who were injured by the blast have been evacuated.
Earlier in the day, a roadside bomb blamed on Taliban militants killed three people, including two members of a prominent provincial political family.
Lala, a tribal elder who goes by one name, his son and their bodyguard were killed on their way to prayers in Helmand Province, about 600 kilometers southwest of Kabul.
Militants have stepped up attacks in recent months in Afghanistan's southern provinces.
RFE/RL Afghanistan Report
SUBSCRIBE For regular news and analysis on Afghanistan by e-mail, subscribe to "RFE/RL Afghanistan Report."