From the Document: "The U.S. government has continued to express concerns about China's record concerning the proliferation of nuclear- and missile-related technologies to other countries, with more recent focus on the threat of Chinese acquisition of U.S.-origin nuclear technology. [...] Official U.S. government reports indicate that the Chinese government has apparently ended its direct involvement in the transfer of nuclear- and missile-related items, but Chinese-based companies and individuals continue to export goods relevant to those items, particularly to Iran and North Korea. U.S. officials have also raised concerns about entities operating in China that provide other forms of support for proliferation-sensitive activities, such as illicit finance and money laundering."
CRS In Focus, IF11737
Congressional Research Service: https://crsreports.congress.gov/