China curbs drug precursor exports ahead of Xi's US visit

China unveiled export restrictions on precursor chemicals that can be used to make drugs on Tuesday, days before a high-stakes meeting between President Xi Jinping and US counterpart Donald Trump.

The rules, announced in a statement by Beijing's commerce ministry, take effect immediately.

They apply to two varieties of substances which will now be subject to applications in order to be exported to the United States, Mexico or Canada, the statement said.

China is the primary origin of precursor chemicals used to make fentanyl, a highly potent opioid underpinning a devastating drug epidemic in the United States.

Shipments of the substances from China have repeatedly complicated the relationship between Washington and Beijing, which has insisted it cracks down heavily on drug trade.

In May, China imposed export controls on another set of drug precursor chemicals shortly after a visit by Trump to Beijing that featured talks with Xi.

Observers will be closely watching this week's visit by Xi to Washington, where he is expected to discuss key topics with Trump spanning trade, artificial intelligence and the US war with Iran.

Trump imposed additional tariffs on Chinese goods last year in retaliation for the country's role in the fentanyl epidemic, but the levies were struck down by the US Supreme Court in February.