A key tenet of the prior Trump administration's crackdown on China and Iran was to punish those Chinese companies caught transferring sanctioned Iranian oil, which was often done through 'ghosting' or at other times offshore ship-to-ship transfers in order avoid detection. 

Since President Biden took office there's been wide reports that China's 'illicit' imports of Iranian oil have soared, resulting in critics and Iran hawks charging the White House with "turning a blind eye" in terms of sanctions enforcement based on existing laws on the books, also as Biden is seeking a path back to engagement with Iran on the US rejoining the JCPOA nuclear deal.

This week a senior Biden admin official has admitted in comments to FT that such banned Iranian oil exports to China have been increasing "for some time now" as Beijing continues to be Tehran's lifeline for circumventing oil sanctions, which has been ongoing for years now. China has also played a major part in keeping Venezuela's oil exports afloat.