A Chinese province has intensified a crackdown on fentanyl precursor trafficking, an issue that strained U.S.-China relations and prompted tariffs on imports from China.

A Chinese province has launched a crackdown on the fentanyl trade — a contentious issue in U.S.-China relations — arresting seven people and shutting down more than 200 websites in recent months, state media reported Thursday.

The announcement came shortly after U.S. President Donald Trump said he would postpone a highly anticipated trip to China because of the Iran War. Trump has used tariffs to try to pressure China to do more to stem the export of fentanyl precursors — the chemical ingredients that go into the synthetic opioid blamed for tens of thousands of overdose deaths annually in the U.S.