BEIJING, March 19 - China has arrested seven people and subjected 12 more to "criminal compulsory measures" in a campaign targeting traffickers in fentanyl precursor chemicals, state media said on Thursday, a move long urged by the United States.

For years Washington had pressed China for measures such as arresting the sellers of chemicals used to make the deadly drug behind thousands of U.S. overdose deaths each year, but it only issued industry notices and took down websites trading in them.