The United States has begun a landmark project to clean up a dangerous chemical left from the defoliant Agent Orange - 50 years after it was first sprayed by American planes on Vietnam's jungles to destroy enemy cover.

Work will now begin to remove Dioxin, which has been linked to cancer, birth defects and other disabilities, from the site of a former US air base in Danang in central Vietnam.

The US sprayed millions of gallons of Agent Orange over the course of a decade.

 Vietnam says several million people have been affected by the toxic defoliant, including more than 150,000 children who have since been born with severe birth defects.

The landmark effort has been heralded as a long-overdue step toward removing a thorn in relations between the former enemies.

It comes nearly four decades after the Vietnam War ended.

The $43 million joint project with Vietnam is expected to be completed in four years on the 47-acre contaminated site, located near Danang's commercial airport and an active Vietnamese military base.

A groundbreaking ceremony took place near the area where a rusty barbed wire fence marks the site's boundary.

US Ambassador David Shear said: “We are both moving earth and taking the first steps to bury the legacies of our past.”

Washington has been slow to respond.

For years officials have demanded more scientific research be carried out to show that the herbicide caused health problems and birth defects among Vietnamese.
Since 2007, it has given about $60 million for environmental restoration and social services in Vietnam, but this is its first direct involvement in cleaning up dioxin, which has seeped into Vietnam's soil and watersheds for generations.

Shear added the US is planning to evaluate what is needed for remediation at the former Bien Hoa air base in southern Vietnam, another Agent Orange hotspot.