China's top quality watchdog announced Tuesday that it had found banned additive clenbuterol, commonly known as "lean meat powder"in China, in some imported pork products this year.

The harmful substance was found in several batches of frozen pork products from the United States, Canada and Denmark in July this year, the General Administration of Quality Supervision, Inspection and Quarantine(AQSIQ) said in a document put on its official website.

Clenbuterol helps to build muscle and is occasionally used as an illegal performance-enhancing drug by track and field athletes. China has banned it as a livestock feed additive as it can cause nausea, dizziness, headaches and heart palpitations in humans.

The unqualified products included frozen pig heads, feet and hearts. Among them, a batch of frozen ham leftovers from the United States was found both mildewy and containing clenbuterol, said the AQSIQ.

All of the tainted products have been returned or destroyed and have never been sold on the domestic market, it said.

In a separate report, the AQSIQ also reported that in August this year, a batch of frozen pig heads from Denmark were found containing salmonella, and Coca Cola China's imports of orange pulp and juice from Turkey was destroyed for poor packaging and illegal importing.