In the latest incident, the Dominican Republic has banned the sale of two brands of Chinese toothpaste for allegedly containing a lethal chemical responsible for dozens of poisoning deaths in Panama last year.

A company under investigation for exporting the toothpaste, Danyang Household Chemical Company, defended its product.

"Toothpaste is not something you'd swallow, but spit out, and so it's totally different from something you would eat," one company manager, who declined to be identified, said by telephone from the eastern province of Jiangsu.

China said on Wednesday it had called on customs officials and directors of its food and quality watchdogs to form an investigative team to probe the toothpaste case.

"Investigations in Beijing and Jiangsu province have been launched into the relevant companies and parties," a notice posted on the Web site of the General Administration of Quality Supervision, Inspection and Quarantine said.

Consumers in the United States have been alarmed by a spate of pet deaths blamed on tainted wheat gluten and rice protein exported from China, as well as reports of toxins and disease in other Chinese exports.

That has helped make food safety the latest flashpoint in often tense trade ties between the nations, who have sparred over everything from piracy to China's currency system.

Vice Premier Wu Yi is in Washington this week for the latest round of dialogue aimed at finding long-term solutions to trade and economic irritants, in particular the United States' frustration over its huge trade deficit with China.

But senior US officials who took part in the talks singled out the safety of Chinese food and medicine as among Washington's "top concerns."

"The Chinese government clearly understands the world marketplace will swiftly disadvantage any nation or economy or firm that is not able to establish a sense of confidence and reliability," Agriculture Secretary Mike Johanns said at the conclusion of two days of high-level talks.

But with US officials pressing for more transparent regulation and for Beijing's permission to send US auditors to China, food safety talks will continue throughout the week.