Chinese officials have long used their willingness to cooperate to stem the flow of fentanyl to the United States as leverage in talks over broader disputes.

In recent weeks, the Trump administration has engaged in direct talks with Chinese counterparts, mostly between the top staff at the Chinese embassy in Washington and the U.S. National Security Council, the four U.S. officials said. Staff at the U.S. embassy in Beijing have also been involved.

A Chinese official is reportedly inquiring about what the Trump administration wants China to do about the ingredients used to make fentanyl.