China has found microscopic worms in wooden packaging from the United States and uncovered substandard U.S. vitamin pills and fish oil for children, Chinese media said on Friday in the latest volley of cross-border accusations.

China has highlighted several quality concerns with U.S. products in apparent response to recent complaints in Washington about the safety of Chinese exports ranging from toys to toothpaste.

The pine wood worms, or nematodes, were found in 13 sets of packaging in the manufacturing hub of Shenzhen, the China Daily said.

Harmful organisms were found in another 10 of 70 batches of wooden packaging sampled between mid-July and mid-August.

This meant the rate of sub-standard packaging from the United States was higher than that for the European Union, Japan, Korea or Canada, the newspaper said.

The labels on some of the wooden packaging were unclear, the report said, adding that that this suggested some exporters might have used fake documents.

Officials have destroyed the goods and urged tighter supervision of wooden U.S. packaging, the paper said.

The vitamin and mineral pills and children's fish oil were discovered in the eastern coastal province of Zhejiang, the China News Service said.

The two failed to reach the nutritious levels promised on their labels, it said, citing the Zhejiang industrial and commercial department.

China recently destroyed a cargo of sub-standard frozen potato slices also shipped from the United States, and the quarantine bureau earlier this month highlighted a cargo of contaminated soybeans that arrived in February.

China has sent a notice to the World Health Organization defending its own food safety standards and said it was willing to cooperate globally to tackle the problem.

China's quality watchdog on Friday introduced what Xinhua news agency called a landmark recall system for unsafe food products and toys to improve product safety.

The regulations, following the introduction of recall system for defective cars in 2005, went into effect on Friday, the General Administration of Quality Supervision, Inspection, and Quarantine announced.

Xinhua did not give details.