U.S. health officials investigating a salmonella outbreak first thought to be linked with raw tomatoes are now examining cilantro and serrano and jalapeno peppers as possible causes.

U.S. Food and Drug Administration spokeswoman Kimberly Rawlings said Saturday evening that officials are testing the ingredients, which are commonly used to make salsa.

Meanwhile, officials with Mexico's Agriculture Department on Monday refuted media reports that suggested the United States is considering blocking produce imports.

"In Mexico there has been no salmonella outbreak in recent months, and definitely not of the type [of salmonella] being seen in the United States," spokesman Marco Antonio Sifuentes told Reuters.

Canadian officials have confirmed that an Ontarian who recently travelled to the U.S. has the same strain of salmonella identified in the American outbreak. A total of 943 cases have been confirmed in the U.S. The same strain of salmonella is also suspected to have been a contributing factor in the death of a Texas man.

Tomato farmers who have been forced to leave their crops rotting in fields and packing houses estimate losses total about $100 million US.

Salmonella bacteria normally live in the intestinal tracts of animals and birds, but can be transmitted to humans if they eat food contaminated with animal feces. Salmonella causes intestinal problems in humans, resulting in diarrhea, fever and cramps.

With files from the Associated Press