The U.S. Veterans advocacy organization “Vet Helping Vets” says the U.S. conducted tests with highly-toxic defoliants in multiple countries, including South Korea, in the 1960s.

According to a government document recently disclosed by the veteran organization, various herbicides that include carcinogenic materials were sent to U.S. bases in South Korea from Fort Detrick in Maryland in July, August and October of 1968.

The document said the transportation of the toxic materials was aimed at testing the effects of repressing growth of plants and trees. The document suggests that the recent finding and the U.S.’s dumping of defoliants in the demilitarized zone in 1968 and 1969 are separate incidents.

The document also said that the U.S. conducted tests involving defoliants or dumped such hazardous materials in Cambodia, Laos and Thailand in the 1960s.