The US has launched a multi-million dollar clean-up operation at an air base in Vietnam it used to store the notorious chemical Agent Orange.
The ten-year programme, unveiled more than four decades after the end of the Vietnam War, will cost $183m (£141m).
The site at Bien Hoa airport, outside Ho Chi Minh City, is considered the most contaminated in the country.
Agent Orange was a defoliant sprayed by US forces to destroy jungles and uncover the enemy’s hiding places.
It contained dioxin, which is one of the most toxic chemicals known to man and has been linked to increased rates of cancers and birth defects.
Vietnam says several million people have been affected by Agent Orange, including 150,000 children born with severe birth defects.
At Bien Hoa the chemical has contaminated the soil and seeped into nearby rivers.
A statement from the US development agency USAID, which is behind the clean-up, described the site as the “largest remaining hotspot” of dioxin in Vietnam.
“The fact that two former foes are now partnering on such a complex task is nothing short of historic,” US ambassador to Vietnam, Daniel Kritenbrink, said at Saturday’s programme launch.