Starting Friday, in order to clear customs, meat importers or their agents who wish to import pork from the US must provide testing reports from qualified testing agencies showing that the meat contains no ractopamine, the Administration of Quality Supervision, Inspection and Quarantine said in a statement released Thursday.

Ractopamine, a feed additive used to promote lean meat, is prohibited for production and sale in China and Russia, but legal for use in feed in the US and Canada.

The quarantine authority in Beijing found ractopamine residues in meat products imported from the US and returned the meat in May 2012.

Russia has banned all beef and pork imports from the US since February 11.