The bus was carrying about 30 people, some of whom suffered serious injuries, police said.
Another report put the death toll at 12, with nine injured, four of them seriously.
The tourists' nationalities were not immediately known, but Rome police said they were not Italian.
The ANSA and Apcom news agencies cited witnesses as saying the tourists were Turkish, but that could not be confirmed.
The crash happened shortly after 11pm local time late on Monday.
A dispatcher at the Rome police headquarters, who said he was not authorised to release his name, said the bus fell about 20 metres into the yard of a private home in northwestern Rome.
He said rescue workers had freed some of the tourists who were trapped in the mangled metal, and were transporting them to area hospitals.