Meat processor JBS said on Wednesday that Beijing blocked US beef shipments from the company's plant in Greeley, Colorado, because traces of the feed additive ractopamine were identified in beef destined for China, reported Reuters. 

Brazil-based JBS, the world's largest beef producer, said in a statement it is working with US and Chinese authorities to resolve the situation and that no other JBS beef facilities in the US have been impacted.

The suspension was effective Monday, according to a notice posted on the US Department of Agriculture's Food Safety and Inspection Service website.

Ractopamine is a feed additive used to boost animal weights. Its use has been banned or restricted in at least 160 countries, including the European Union, Russia and China.

Earlier this year, major food safety, environmental and animal rights groups filed a lawsuit against the US Food and Drug Administration, seeking to force it to reconsider approvals of ractopamine, which they say is putting human health at risk and causing stress in farm animals prior to slaughter.

In addition, China has blocked meat and poultry products coming from the Cool Port Oakland in Oakland, California, effective the same date, according to the USDA site. Cool Port Oakland is a cold storage facility, used for storing perishable or other sensitive goods like food or medicine.

The restrictions sent Chicago Mercantile Exchange cattle futures slumping on Wednesday, analysts said, with the most-active August live cattle contract posting its biggest percentage drop since May 1.

Officials from Cool Port Oakland could not immediately be reached for comment on Wednesday. USDA officials had no immediate comment.