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

Dioxin, which has been linked to cancer, birth defects and other disabilities, will be removed from the site of a former U.S. air base in Danang in central Vietnam. The effort is seen as a long-overdue step toward removing a thorn in relations between the former foes nearly four decades after the Vietnam War ended.

"We are both moving earth and taking the first steps to bury the legacies of our past," U.S. Ambassador David Shear said during the groundbreaking ceremony near where a rusty barbed wire fence marks the site's boundary. "I look forward to even more success to follow."

The $43 million joint project with Vietnam is expected to be completed in four years on the 19-hectare (47-acre) contaminated site, now an active Vietnamese military base near Danang's commercial airport.

Washington has been quibbling for years over the need for more scientific research to show that the herbicide caused health problems among Vietnamese. It has given about $60 million for environmental restoration and social services in Vietnam since 2007, but this is its first direct involvement in cleaning up dioxin, which has seeped into Vietnam's soil and watersheds for generations...