The US Treasury Department has imposed sanctions on 40 shipping companies and vessels, as well as a Chinese oil refinery, amid concerns over secretive oil trade between Beijing and Tehran.
Ahead of a Trump-Xi summit, the move is seen as an effort to curb the flow of Iranian oil to China, which has been increasing in recent months.
The sanctions target companies and vessels involved in the transportation of Iranian oil, including those that have been accused of evading US sanctions by using complex financial transactions and shell companies.
The US Navy has also been patrolling the Arabian Sea to monitor Iranian-flagged cargo ships, such as the Touska, which was intercepted on April 20.