CHICAGO -- Russia has halted pork shipments from six U.S. sources, including a Smithfield Foods meat-processing plant, saying their products failed to comply with import requirements, according to the U.S. Department of Agriculture.

Russia, the fourth-largest buyer of U.S. pork, will not accept shipments from the plants after Dec. 15, the USDA's Food Safety and Inspection Service said in a Dec. 2 statement. The suspensions follow visits by Russian government officials in October as part of an annual audit, said Amanda Eamich, an FSIS spokeswoman.

"They gave us a letter stating that these plants didn't comply with Russian requirements," Eamich said in a telephone interview from Washington. "They haven't provided any additional information."

Russia has halted or plans to stop pork shipments from 10 U.S. processing plants and slaughterhouses this year, Eamich said.

Smithfield spokesman Jerry Hostetter confirmed that one of the company's plants will be affected by the latest suspension. He declined to say how much it ships to Russia.

"We always regard these matters as much more political than scientific," Hostetter said.

The other meat-processing plants affected by the recent suspension are run by the Chicago Meat Authority and Amity Packing in Chicago, Farmington Foods in Forest Park, Illinois, and Abilene TX Foods in Jeffersontown, Kentucky. The suspended slaughterhouse was identified as Sioux-Preme Pork Products in Sioux City, Iowa.

Last month, Russia said it planned to cut pork imports by 200,000 tons next year in an effort to boost domestic production. The country imported 162.2 million kilograms of U.S. pork this year through September, more than twice as much as a year earlier, USDA data show.