BEIJING (AP) -- Wal-Mart pulled a brand of eggs from all its stores in China on Tuesday after tests in Hong Kong found they were tainted with the same toxic chemical blamed for sickening tens of thousands of babies.
The discovery of melamine in eggs raises more questions about how far the chemical at the center of China's tainted milk scandal has penetrated the nation's food chain.
Wal-Mart, the world's largest retailer, said it had removed the "Select" brand of eggs produced by China's Dalian Hanwei Enterprise Group from its shelves in China. A government official in Dalian, the northeastern port city where Hanwei is located, said the company had begun a nationwide recall of the suspect eggs.
Mu Mingming, a spokeswoman for Wal-Mart, said the company was working closely with suppliers and the government. "We just want to make sure the products on our shelves are safe," Mu said by telephone from Shenzhen.
Hong Kong testers found melamine in the eggs at nearly two times the territory's legal limit for the chemical in food. The egg contamination has prompted Hong Kong officials to expand testing to Chinese meat imports.
Wal-Mart and Chinese officials said they did not have a figure for how many eggs had been recalled and it was not immediately clear which countries import eggs from China. So far, no illnesses have been reported.
It remains unclear what eating melamine-tainted eggs will do to humans. But in the milk scandal, infant formula heavily contaminated with the chemical caused kidney stones and other kidney ailments in 54,000 children and was blamed in the deaths of four babies. More than 3,600 children remain sick, health officials say.
Hanwei's director, Han Wei, apologized for the contamination.
"There are no consumers asking about protein levels in our eggs and so there is no need for us to add melamine to our eggs in the process of selling our products," Han told the Hong Kong television station TVB Tuesday. "We truly regret this. We too have an undeniable responsibility."
Han did not explain how the chemical made its way into the company's eggs. But the Chinese Agriculture Ministry's animal husbandry department head, Wang Zhicai, said it was likely added to chicken feed, the Beijing News reported.
The newspaper said the ministry has been inspecting feed for the chemical since last year, after a Chinese-made pet food ingredient laced with melamine was linked to the deaths of dozens of dogs and cats in the United States and touched off a massive pet food recall.
Melamine is used in making plastics and fertilizer, and is banned from animal feed. A food industry expert said it was likely added for the same reason cited in the milk scandal and last year's pet food recall: Melamine boosts nitrogen levels, making products seem higher in protein when tested.
Jason Yan, the U.S. Grains Council's technical director in Beijing, said the chemical could have been added by suppliers trying to pass off a normal-grade protein ingredient as a higher-grade product.
He said that in soybean meal, for example, the price gap between the regular and premium grades is around $30-$50 per ton.
"Some traders may be willing to take the risk by adding melamine to make a lot more profit," he said.
Chinese media reports said major Chinese retailers in the southern province of Guangdong, which borders Hong Kong, have also stopped selling the suspect eggs.
An official with Dalian city government said Hanwei had started a nationwide recall of eggs deemed "problematic." The official, who refused to give her name as is common in China, said she had no further details.
Associated Press researcher Xi Yue contributed to this report in Beijing.