LOS ANGELES - THE source of the Salmonella that has sickened hundreds of people through tainted tomatoes may be in Mexico and South and Central Florida, United States investigators said.

Health officials said on Friday all indications pointed to a single geographic region as the source of the outbreak, which has sickened 228 people in 23 states.

Mr David Acheson, associate commissioner for foods at the US Food and Drug Administration (FDA) said on a conference call that nine people who became ill with Salmonella had eaten at two different outlets of the same restaurant chain. He declined to name the chain or the location of the restaurants. 'That represents a small cluster within this outbreak,' he said.

The FDA has linked the outbreak to raw round, plum and Roma tomatoes, and has issued a list of states and countries whose tomatoes are not associated with the outbreak.

California, Georgia, New York, Canada, Guatemala and the Dominican Republic are among tomato producers on the safe list.

The FDA also has cleared counties in North Florida, whose tomatoes were not widely available at the time of the outbreak.

The FDA said investigators were focusing on South and Central Florida and Mexico because they were the biggest producers at the time.

The Mexican government said earlier this week that its tomatoes were being unjustly targeted, adding that the uncommon Salmonella Saintpaul bacteria identified in the outbreak has never been found in Mexico.

Shipments from Mexico have been stopped at the border, flooding Mexico's market with tomatoes.

The Florida Tomato Committee said on Thursday the state's industry remained committed to production of a safe product. It said Florida was the first state in the country to adopt a comprehensive food safety programme with mandatory government inspection and audit of its tomatoes. -- REUTERS