China has found many safety problems from soybeans imported from the United States and urged the US authorities to improve quality of soybean exports.

Local entry-exit inspection and quarantine bureaus have discovered many quality and safety problems from US-imported soybeans, said the General Administration of Quality Supervision, Inspection and Quarantine (GAQSIQ) on its website.

Inspection and quarantine units often find hazardous weeds such as sorghum halepense and iva xanthifolia that could threaten China's farm production, forestation and ecological safety. The imported soybeans also had soil clods containing pest which poses threats to China's soybean production, it said.

In February, quality watchdogs found pesticide residue in soybeans imported from the United States, it said.

Some soybeans imported from the United States failed to reach the requirement in protein and oil contents, and had more impurities than as required in contracts.

"These problems indicate loopholes in process of growing, harvesting, storing, transporting, inspecting and quarantining soybeans in the United States," it said.

The administration has notified the US authorities and demanded an investigation into the case and effective measures to avoid similar problems.

It also vowed a closer monitoring on imported soybeans and more negotiations with overseas counterparts.

In recent years, China has been importing millions of tons or more of transgenetic soybeans from the United States.

China announced on Monday it had returned 272 heart pacemakers imported from the United States after they failed quality inspections.