Simone Camilli, 35, was a video journalist who had been with the Associated Press since 2005. Also killed were his Palestinian translator, Ali Shehda Abu Afash, the head of the bomb squad, Taysir Al Houm, and two Gaza police officers, the AP said.
Four others, including AP photographer Hatem Moussa, were badly injured.
The explosion occurred when a bomb disposal crew attempted to move unexploded munitions in the town of Beit Lahiya, a scene of fierce fighting between Israelis and Hamas in the northern Gaza Strip during the month-long conflict.
A three-day cease-fire, which went into effect Monday, has given Gazans an opportunity to rebuild and search for live ordnance like that which exploded Wednesday.
The cease-fire is scheduled to end at midnight Wednesday (6 p.m. EDT) if an agreement isn't reached during ongoing negotiations in Cairo.