US food safety officials said they were seeking more information from Beijing to establish whether the failure of health supplements, raisins and pistachios to meet Chinese safety standards were "bona fide, science-based findings" or retaliation for US actions. China said on Friday that inspectors at the ports in Ningbo and Shenzhen had found bacteria and sulfur dioxide in products shipped by three American companies, AP reported. Then on Saturday, inspectors in Guangdong province rejected a two-ton shipment of pistachios because they contained "milky white ants", which looked similar to termites. "It is tit-for-tat? We don't know and probably won't ever know," said Dr David Acheson, the US Food and Drug Administration's assistant commissioner for food protection. US inspectors have recently banned or rejected a number of Chinese exports on safety grounds, including contaminated monkfish, frozen eel and juice. It has also stopped all imports of Chinese toothpaste after a potentially deadly chemical was found.