China has intensified efforts to ensure food safety after a spate of incidents involving poisonous pet feed in the Untied States.

The State Council yesterday issued a circular ordering inspections of medicines and additives used in animal feed to be carried out nationwide.

The General Administration of Quality Supervision, Inspection and Quarantine the top quality control watchdog said on Tuesday that two Chinese companies had exported melamine-contaminated wheat gluten and rice protein blamed for the deaths of dogs and cats in the United States.

Xuzhou Anying Biologic Technology Development Co Ltd and Binzhou Futian Biology Technology Co Ltd "illegally added melamine to wheat gluten and rice protein in a bid to meet the contractual requirement for the amount of protein in the products," it said.

The firms evaded quality checks by labeling the products as export items, which are not subject to domestic quality inspections.

It added the local public security authorities had launched an investigation into the cases and had detained company officials.

The administration said it had found no more melamine-contaminated products after checking 399 samples from 173 exporters nationwide.

The watchdog said it had notified the US Food and Drug Administration (FDA) of the investigation results and proposed to set up a cooperation mechanism on food safety with the United States.

Melamine is an organic chemical used in the production of a wide range of products including glues , resins and fertilizers.

When added to foods it makes them appear more protein-rich, but it can be deadly to animals, according to the FDA.

Melamine is not believed to pose a risk to humans.

So far 15 deaths of dogs and cats have been reported by the FDA, which, however, is investigating the deaths of hundreds of pets, according to Reuters.

A team from the US Food and Agriculture department has reportedly arrived in China to help with investigations.

Meanwhile, Washington is considering a ban on imports of wheat gluten and rice protein from China, according to media reports.

In another development, several US states have recently banned catfish from China because of the presence of a potentially hazardous antibiotic named fluoroquinolone banned by the FDA.

However, it is in accordance with domestic standards, an official with the Ministry of Agriculture said yesterday.