A United Nations agency says amphetamine-type stimulants, or ATS, are now the number-one illicit drug threat facing East and Southeast Asia.

The U.N. Office on Drugs and Crime says in a report Tuesday that methamphetamine seizures increased fourfold in the Greater Mekong countries of Laos, Burma, Thailand and China between 2008 and 2010. It says ATS now present a greater threat than plant-based drugs like heroin, opium and cannabis.

The report says the drugs are primarily manufactured in in China, Burma and the Philippines, but that crystal methamphetamine and ecstasy are now being made in Indonesia and Malaysia as well. It identifies new ATS trafficking routes, including one along the Mekong River through Burma, Thailand, China, Laos and Cambodia.

The report says the stimulants are also being trafficked to the region by organized criminal gangs from Africa and Iran.

It says that on a global basis, ATS are now the second most widely used illicit drugs after cannabis.