China's quality control watchdog has announced two Chinese companies exported melamine-contaminated wheat gluten and rice protein blamed for the deaths of dogs and cats in the United States.

The US Food and Drug Administration (FDA) earlier said the Xuzhou Anying Biologic Technology Development Co. Ltd. and Binzhou Futian Biology Technology Co. Ltd. had exported the melamine-tainted products.

The FDA discovered melamine, a chemical used in plastics, fertilizers and flame retardants, in pet food recalled by Ontario-based pet food maker Menu Foods and traced the contaminated foodstuff to the two Chinese companies.

"The two companies illegally added melamine to the wheat gluten and rice protein in a bid to meet the contractual demand for the amount of protein in the products," said the General Administration of Quality Supervision, Inspection and Quarantine.

The watchdog said the two companies managed to evade quality check-ups by labeling them as exports that are not subject to quality inspection.

It said it had ordered local branches to strengthen quality inspection on all vegetable proteins and pledged to include all vegetable proteins on the exports list subject for quality check-ups.

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

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

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