In an import alert, the FDA said it had given inspectors the power to detain without inspection all vegetable protein imports from China for use as animal or human foods if they suspect the products might contain melamine.

Facing increasing criticism for its handling of food safety incidents, the FDA has beefed up its regulatory oversight of the industry. Just this week the FDA created a new regulatory position to solely oversee food safety and protection.

The regulatory guidance on melamine was issued in the wake of a contamination scare after hogs and chickens meant for human consumption were fed pet foods thought to contain the chemical.

The US Department of Agriculture said Tuesday that pet food made with contaminated wheat gluten from China was mixed into feed used on 30 broiler chicken farms in Indiana. About 3m chickens fed the feed have all been processed and sold on the market.

The FDA said it has no evidence that humans have suffered any health problems after eating the processed products made from the hogs and poultry.

In is import alert guidance the FDA singled out a number of wheat, rice, corn, soy and mung bean imports from China for regulatory attention. Any increase in detention could mean some processors will find their ingredient imports are not available when they need them.

Over the past few weeks, melamine contamination was linked to an outbreak of cat and dog deaths and illness associated with pet food manufactured with vegetable proteins from China.

About 18 pet food manufacturers and others have recalled dog and cat food and other suspect products and ingredients. The FDA noted that it had collected about 750 samples of wheat gluten and products made with wheat gluten.

Of these 330 tested positive for melamine or melamine related compounds. Of the 85 samples of rice protein concentrate and products made with the ingredient, 27 tested positive. All the ingredients were imported from China.

China has since banned its food exporters from using melamine.

Melamine is a chemical compound used in a number of commercial and industrial applications. The US has banned its use as an ingredient in animal and human foods. It has limited authorisation for use in contact materials such as packaging for human food.

The FDA said since the extent of the problem is not known in China it was assigning its inspectors the immediate powers to make detentions.

The FDA is also continuing an investigation after the California Department of Food and Agriculture (CDFA) said laboratory testing had detected melamine in urine from hogs at a farm in Ceres.

The findings could potentially further raise consumer fears over the safety of the food chain, even as Congress is examining whether the FDA failed to prevent recent contamination outbreaks linked to spinach and lettuce.

The 1,500 hogs at the American Hog Farm have been quarantined while the CDFA conducts additional testing to determine if melamine is present in meat.

The American Hog Farm operates a sizable part of its business through a "custom slaughterhouse," which processes animals on-site and sells them to individuals for personal use and not for resale.

Melamine is sometimes used to illegally boost the protein content of foods.

This week, the FDA appointed David Acheson to fill the new role of assistant commissioner of food protection. The FDA said he will develop "an agency-wide, visionary strategy for food safety and defense".

Acheson is a former chief medical officer with the FDA's Centre for Food Safety and Applied Nutrition.