The United States has begun cleaning up the contamination left from the herbicide Agent Orange sprayed by U.S. forces during the U.S.-Vietnam War, nearly four decades after the conflict ended.

Vietnamese and U.S. officials launched a project Thursday to clean up deposits of the toxic chemical dioxin at a former U.S. airbase in Danang where Agent Orange was stored and handled during the war.

The U.S. dumped millions of liters of Agent Orange on Vietnam's thick jungles during the war to clear vegetation in search of Vietnam's communist forces.

But in addition to destroying millions of acres of vegetation, the herbicide is also thought to have had unintended consequences. Exposure to the chemical has been linked with respiratory cancer, diabetes and birth defects.

U.S. Ambassador to Vietnam David Shear said at a ceremony Thursday the joint cleanup project is a “landmark moment” that shows Hanoi and Washington are “taking the first steps to bury the legacies of our past.”

The decontamination effort, which will last until 2016, involves testing and gathering about 73,000 cubic meters of affected soil and heating it to a high temperature to burn off leftover dioxin.

The U.S. Agency for International Development (USAID) is overseeing the cleanup of Danang, which is the most seriously contaminated of the 28 locations where dioxin has been found.

Other former U.S. airbases where Agent Orange was stored are expected to be cleaned up during the next decade.