Several factors influence the current status of China in international drug trafficking. These include history, location, size, population, and current economic conditions. Many of the individuals involved in the international trafficking of Southeast Asian heroin are members of ethnic Chinese groups, some of which reside outside of China. Chinese officials indicate that the majority of heroin entering China comes over the border from Burma. Southwest Asian heroin enters northwestern China from Afghanistan, Pakistan, and Tajikistan. China is a major source of precursor chemicals necessary for the production of cocaine, heroin, and crystal methamphetamine. Reports indicate that acetic anhydride is diverted from China to morphine and heroin refineries in the Golden Triangle. China is also a leading exporter of bulk ephedrine imported into Mexico; these precursor chemicals are subsequently used to manufacture methamphetamine destined for the United States. Although China has taken aggressive actions through legislation and regulation of production and exportation of precursor chemicals, additional action is required to control the illicit diversion and smuggling of precursor chemicals. China is a party to the 1988 U.N. Drug Convention, the 1961 U.N. Single Convention as amended by the 1972 Protocol, and the 1971 U.N. Convention on Psychotropic Substances. China also participates in a drug control program with Iran, Pakistan, Tajikistan, Turkmenistan, Uzbekistan, Russia, and the United States.