China’s quality watchdog agency announced over the weekend that it was suspending some imports from seven U.S. companies, including giants Cargill Meat Solutions and Tyson Foods.

The agency said that Tyson’s frozen foods were tainted with salmonella and that Cargill’s pork ribs contained a feed additive approved in the U.S. but not China.

Both companies responded guardedly.

Tyson said it had received no notification from the Chinese government about the ban, and Cargill said the manufacturer was already seeking approval for the banned substance.

“We will work with the U.S. and Chinese governments to get this matter resolved,” said Tyson spokeswoman Libby Lawson.

The suspension was the latest strike in a widening skirmish that began in March after contaminated pet food ingredients from China sickened thousands of dogs and cats in the United States.

Since then, U.S. food regulators have restricted imports of Chinese shrimp, eel, catfish and other seafood, citing concerns about carcinogens or residues of antibiotics.

China has sent back U.S. shipments of dried apricots, raisins and a sugar-free drink mix that regulators said had too much red dye.

On Sunday, the American Chamber of Commerce in China, whose members include Cargill and Tyson, responded to the suspension with a statement saying that blocking the foods would be proper if based on substantiated facts.

The statement, by the chamber’s president, James Zimmerman, also urged China to increase product quality and protection for consumers.

“We do not believe a trade war is imminent,” he said. “Both sides have challenges to ensure that consumer health and safety ... is given first priority.”