Wal-Mart Stores Inc., the world's largest retailer, said Wednesday it will set new quality standards for its suppliers, following a series of scandals involving Chinese-made products, which account for a major portion of the company's sales.

Meanwhile, the United Nations recommended China increase oversight of its food safety system and hold businesses accountable for their products, amid the latest scandal involving tainted milk products that have killed several babies and sickened tens of thousands across China.

Mike Duke, vice chairman of Wal-Mart Stores Inc.'s international division, said the company has been working on the initiative for three years, but recent scandals over the quality of Chinese-made products have made transparency in the supply chain "even more important."

"We have to ask all our suppliers to take full responsibility," Duke told The Associated Press. "Not ... just the factories or final production, but to go all the way upstream to look at any products, any raw materials that go in the products."

While Duke said the new standards applied to all products, confidence in Chinese products has been sagging after high levels of industrial toxins were found last year in exports ranging from toothpaste to toys.

In 2007, melamine was found in a Chinese-made pet food ingredient and blamed in the deaths of dozens of dogs and cats in North America.

In August 2007, Wal-Mart quietly began pulling two brands of dog treats from its shelves after tests found they contained traces of the industrial chemical melamine. The Bentonville, Ark.-based retailer began the tests after several customers complained about the items sickening their dogs.

Later that year, Mattel Inc. recalled more than 21 million Chinese-made toys worldwide because they contained lead paint or tiny, detachable magnets that might be swallowed.

Wal-Mart also sold Chinese-made cribs which were part of a recall this week by New York-based Delta Enterprises. The cribs were recalled because of the potential for missing safety pegs.

China is still reeling from the revelation last month that melamine, used to make plastics and fertilizer, was added to infant formula to artificially boost nitrogen levels and make it seem higher in protein when tested.

Melamine-laced baby formula has been blamed for the deaths of four babies and sickening another 54,000 children.

Contamination has since turned up in powered and liquid milk, yogurt and other products made with milk. Dozens of countries have pulled Chinese-made goods with dairy ingredients off their shelves to test for melamine.

Earlier, in remarks at a Wal-Mart sponsored conference on sustainability and manufacturing in Beijing, Duke said starting next month suppliers will be required to "tell us the name and location of every factory they use to make the products we sell."

"Essentially, we expect you to ask the tough questions, to give us the answers and, if there's a problem, to own the solution," told suppliers at the conference.

In a report released Wednesday, the United Nations recommended China tighten oversight focusing on high-risk areas of the food chain, have an all-encompassing food safety law that would cover the whole industry and hold businesses responsible for the products they sell.

"The national system needs urgent review and revision," said Khalid Malik, the U.N. resident coordinator in China.

Additionally, China needs a unified regulatory agency, the report said, and a place consumers can go for reliable information. The task is currently split between different government agencies, creating uneven enforcement that is further complicated by numerous laws.

In Macau, government officials said late Tuesday three more children have developed kidney stones, bringing the total number of sick children to seven in the southern Chinese territory.