The country's top quality watchdog on Friday said it had returned 460 tons of soybeans imported from the United States because they contained live Khapra beetles - an extremely destructive pest of grain products and seeds.

The soybeans, in 21 containers, were seized at Huangpu Port in Guangzhou, Guangdong Province, according to a circular from the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ).

"It's the first time that China found such a pest in imported soybeans," the circular said.

The Khapra beetle is considered one of the world's most serious pests to stored grain products, such as wheat, rice, corn and broomcorn, as well as beans and nuts.

Media reports said that the beetle may cause grain damage of up to 30 percent, although 75 percent damage has also been reported. The beetle is mainly spread by trade, because it cannot fly.

The AQSIQ also said in the circular that the US soybeans also contained some other live pests and weeds that could threaten local agriculture.

"According to laws and regulations, we've decided to return the soybeans and suspend the import from The Scoular Company, the supplier," the circular said.

It said the batch of soybeans had received official inspection and quarantine certificates from the United States, so AQSIQ had asked the US side to investigate and improve its export inspection and quarantine processes.

The Scoular Company, according to its website, is a century-old agricultural marketing company with annual sales of $2 billion.

It is not the first time China has reported problematic soybeans from the US. Late last month, the AQSIQ said that it had recently found "substantial" quality-related problems with imports of US oilseed. It said soybeans shipped from the US often contained harmful weeds, or herbicide residue.

Soybeans, which are mainly crushed for oil and used as animal feed, are the biggest single US farm export to China, according to the American Soybean Association.

Last year, more than 10 million tons of soybeans were exported from the US to China.

Apart from soybeans, the AQSIQ had also reported unsafe food, pacemakers, wooden packaging, and mechanical and electrical machines from the US in the past few months.

Some foreign media said the moves are knee-jerk reactions to the recent American reports on unsafe Chinese products, including seafood, tires and toys. However, the Chinese authorities denied the claim, saying that all the moves are normal practice according to rules and regulations. (By Zhu Zhe)