KANSAS CITY — U.S. commodity markets retreated Monday in part on fears related to the outbreak of swine flu, potential reduced pork consumption and the banning of pork imports from the United States by Russia, China and other countries, although there have been no reports of the virus in U.S. swine.

Some lean hog futures contracts traded at the Chicago Mercantile Exchange fell the daily trading limit on Monday, with pork belly and cattle futures also sharply lower. Grain and oilseed futures also tumbled, largely on speculative selling, as fears that any potential dent in pork demand would stymie feed demand, with corn and soybean meal the primary energy and protein sources for U.S. hog herds.

Concern about planting delays for U.S. corn because of wet weather provided some offset to swine flu concerns, trade sources said.

Other commodity and equity markets also fell, especially airline and transportation stocks, as news of more outbreaks of the virus spread. Several companies across the world restricted travel, especially to Mexico where the outbreak initially occurred.

"Let me say again to consumers, there is no evidence at this time that U.S. swine have been infected with this virus," U.S. Department of Agriculture secretary Tom Vilsack said in an update Monday.

"I want to reiterate the same message to our trading partners — our pork and pork products are safe," Mr. Vilsack said. "The discovery of this virus in humans is not a basis for restricting imports of commercially produced U.S. pork and pork products, Any trade restrictions would be inconsistent with World Organization for Animal Health guidelines. U.S.D.A. is working closely with the U.S. Trade Representative’s office on these matters."

The virus has been confirmed in at least seven countries with suspected cases in several more. In Mexico about 150 persons have died and more than 1,000 have been infected. Outbreaks also have been reported in the United States, Canada, Israel, the United Kingdom, Spain and New Zealand, with possible cases in Australia, France, Germany, Sweden, Norway and South Korea, according to press reports. No deaths have been reported in any country except Mexico.

"U.S.D.A. already has in place, and did so before last week’s events, a surveillance system to monitor animal health," Mr. Vilsack said. "I asked U.S.D.A. to reach out to agriculture officials in every state to affirm that they have no signs of this virus type in their state’s swine herd. As of this morning (Monday), no cases have been reported.

"It is important to remember that not only have there been no reports of this virus in swine, according to scientists at U.S.D.A., swine flu viruses are not transmitted by food so a person cannot get swine flu from eating pork or pork products. In fact, cooking pork to an internal temperature of 160 degrees Fahrenheit kills all viruses and other foodborne pathogens. Eating properly handled and cooked pork or pork products is safe."

The World Health Organization has not called the situation pandemic, but has raised its alert to phase four out of six because the flu spreads easily.

The new strain consists of a mixture of genetic material from swine, avian and human influenza viruses, the U.S.D.A. said.

According to the Centers for Disease Control, swine flu may spread through contact with infected pigs or environments contaminated with swine flu viruses and through contact with a person with swine flu.

There currently is no vaccine, although the virus has been isolated.