China said on Wednesday it had stepped up inspections of key US imports such as pork and automobiles, just as a high-level delegation visits Washington for key trade negotiations.
The world's two largest economies are locked in a tense standoff with tariff threats hanging over billions of dollars of goods many fear could spark a damaging trade war between the economic superpowers.
Vice Premier Liu He, President Xi Jinping's top economic adviser, and central bank chief Yi Gang arrived in the US capital on Tuesday for a new round of talks aimed at heading off a trade war.
Hopes the two sides can reach a deal were raised at the weekend when President Donald Trump said he was working with Xi to prevent telecom giant ZTE from going out of business after it was hit by a US technology sales ban.
However, Commerce Secretary Wilbur Ross has said there was a "wide" gap between the US and China while lawmakers in Washington questioned the offer to prevent ZTE's collapse, citing national security issues.
Meanwhile, Beijing has taken action to show their US counterparts the value of access to China's market for American goods and firms.
"We increased the inspection ratio of American pork," China's customs bureau said in faxed comments to AFP, calling the practice "in line with international norms."
It added that inspections came after "we found there were problems with American pork", the department said without providing details.
Reports have also said inspectors are taking similar action against US car giants such as Ford, waste imports, among other products.
The customs administration said US car imports were quickly deteriorating in quality when AFP queried the regulator about holdups for Ford.
"In the first four months of the year, major car ports in China detected a total of 652 batches of cars from the US -- totalling 4,360 vehicles worth $312.5 million -- that were not up to standard," the customs administration said.
"This is a relatively quick pace of growth," the regulator said.
A spokesman for Ford said: "We are closely monitoring our situation at the port."
The moves against waste imports have thrown the American recycling industry into a tailspin as China was one of the most important destinations for US trash.
On May 3, China said it would inspect all US waste coming into the country, according to a Chinese customs notice reposted by a US recycling trade group.
Citing statistics showing US waste imports failing to meet standards, China's customs department said it took action to "protect people's lives and health and safeguard the ecological environment".
"The United States has become the largest source of solid waste materials that do not meet environmental or major quarantine standards, so the risk attached to importing its waste materials is obviously high."
It denied any of the action targeted a specific country.
In a meeting with US business leaders in Beijing, Vice President Wang Qishan struck a more conciliatory tone.
"Economic and trade relations are the ballast of the the two nations' relations, and their essence is cooperatively beneficial," he said, according to the People's Daily.