The US has started a project to clean Agent Orange left over from the Vietnam War 40 years ago.
The £30 million joint project will clear a former US air force base, which was used to store and mix the chemical weapon.
Millions of gallons of the toxin were sprayed to defoliate vast swathes of jungle and rob Vietcong fighters of cover.
The toxin is thought to have seeped into the soil, causing cancer and birth defects in the local population.
The US has been reluctant to accept that the toxin is responsible for the problems, claiming that more research needed to be done, but has now decided to act.
“This morning we celebrate a milestone in our bilateral relationship. We’re cleaning up this mess.” said David Shear, the US ambassador, at the inauguration of the four-year project.
"We are both moving earth and taking the first steps to bury the legacies of our past,"
The use of Agent Orange by the US is still a cause for bitterness among Vietnamese, especially as the US has rejected calls for reparation for several years.
A court case brought against the US manufacturers by a group of victims was rejected in 2007.
“It’s a big step,” said Ngo Quang Xuan, a former Vietnamese ambassador to the United Nations. “But in the eyes of those who suffered the consequences, it’s not enough.”
Agent Orange Victims Association Vice Chairman Tran Xuan Thu told the BBC that although the clean-up activities were "a little late", they were "greatly appreciated".
"They show that the US government now is taking the responsibility to assist us. I hope these efforts will be multiplied in future," he said.
"However we consider that the clean-up is separate from the issue of compensating Vietnamese Agent Orange victims, who are still suffering from injustice. These victims will carry on with their lawsuits, no matter what."
