The officials said the bus was traveling Friday in the Marioutiyah area near the pyramids when the roadside bomb went off.
There was no immediate word on the nationalities of the tourists onboard, but the officials said one of those killed was an Egyptian.
The officials spoke on condition of anonymity because they were not authorized to brief the media.
Egypt has battled Islamic militants for years in the Sinai Peninsula in an insurgency that has occasionally spelt over to the mainland, hitting minority Christians or tourists. However, this is the first attack to target foreign tourists in almost two years.