The United States has asked the United Nations to classify two chemicals used to make fentanyl as controlled substances, The Wall Street Journal reports.

U.S. Secretary of State John Kerry wrote a letter to U.N. Secretary-General Ban Ki-moon, asking that the ingredients be added to a list of controlled substances in a U.N. convention that regulates narcotics. If the chemicals are added to the list, countries would be required to monitor their export and inform recipient nations of any planned shipments, the article notes. Nations also would have to seize shipments that appeared linked to illegal production of a narcotic drug.

Drug cartels are selling lethal doses of fentanyl disguised as street heroin and counterfeit OxyContin pills, two U.S. government agencies warned earlier this month. Just a few grains of fentanyl can be lethal, the agencies said.