(Reuters) - The U.S. Commerce Department on Monday added three companies in China to a list of firms receiving U.S. exports that officials have been unable to inspect.

Companies are placed on the "Unverified List" when U.S. export control officers cannot complete on-site visits to determine whether they can be trusted to receive U.S.-origin technology and other goods.

U.S. inspections of Chinese companies require the approval of China's commerce ministry. U.S. exporters are required to conduct additional due diligence before sending items to companies on the list, which serves as a red flag, and may have to apply for more licenses.

(Reporting by David Shepardson)