WASHINGTON (Reuters) – U.S. health officials urged consumers on Friday to avoid only raw jalapeno peppers from Mexico, narrowing an earlier warning against eating any fresh jalapenos amid an outbreak of salmonella illness.

The Food and Drug Administration now believes jalapeno and serrano peppers grown in the United States are not connected to the nearly 1,300 salmonella cases reported since April, Dr. David Acheson, FDA associate commissioner for foods, told Reuters in an interview.

Investigators seeking the source of the outbreak have been probing clusters of illnesses in various locations.

“All the ones we have been looking at have been traced back to Mexico,” Acheson said.

Officials are trying to pinpoint a particular region or farm as the source of the contamination, which came from a strain known as Salmonella stpaul, he added.

Investigators had focused early in the probe on tomatoes as a possible culprit. Last week, regulators lifted their warning on tomatoes not because they were cleared from suspicion, but because any that could have been contaminated would have spoiled and been discarded by that time.

“Available data does not exonerate tomatoes at this point,” Dr. Ian Williams of the Centers for Disease Control and Prevention said.

Enrique Sanchez, the director of Mexico’s National Sanitation and Farm Food Quality Service, called the decision “arbitrary” and said it could have an “enormous” harmful impact on the local jalapeno industry.

“The FDA is taking a decision without scientific proof,” Sanchez told Reuters. “In Mexico there is no outbreak reported by the health ministry that indicates, not even suspiciously, that there is a salmonella outbreak in Mexico.”

Mexican officials will conduct their own investigation, said Marco Antonio Sifuentes, a spokesman for the Mexican agriculture ministry. Mexico says the Salmonella stpaul strain has not been detected in the country.

“We have said it so many times that we’re tired of repeating it. There does not exist one single case of Salmonella stpaul in Mexico,” Sifuentes said.

The agriculture ministry said it has seen no scientific evidence from U.S. authorities that the tainted jalapenos originated in Mexico.

“In the case of tomatoes, the FDA made a serious error. Now they are committing another big mistake because of their incompetence,” Sifuentes said.

The FDA’s Acheson said U.S. officials were working closely with Mexican authorities on the investigation.

Food safety experts say finding the outbreak’s source has been difficult because people had trouble recalling what they had eaten before they became ill and the produce had been discarded by the time inspectors could follow up.

Serrano peppers have also been scrutinized as a possible source. The FDA still advises the elderly and people with weak immune systems to avoid eating raw serrano peppers from Mexico, Acheson said.

On Monday, the FDA said a single jalapeno pepper at a Texas distributor was contaminated with the strain of salmonella detected in the outbreak. That pepper originated in Mexico. The FDA said on Friday it had determined the contamination did not originate at the Texas distributor.

The latest salmonella illness was reported to have occurred on July 10, bringing the total to 1,294, Williams said.

Cases have been reported in 43 states, the District of Columbia and Canada, and 242 people have been hospitalized.

Salmonella poisoning, which causes diarrhea, fever and abdominal cramps is very common, with 40,000 cases and 400 deaths each year in the United States alone.