U.S. forces sprayed Agent Orange over a wide area of Vietnam during the war that ended in 1975 in a bid to deprive Communist soldiers of food and jungle cover. Its use was stopped in 1971 after it was found to contain the known carcinogen, dioxin.
"We should not and cannot wait while the scientists continue to debate," Barry Weisberg, of U.S. not-for-profit group Violence Prevention and Peace Promotion Strategy, said at a gathering of health and environment experts in Stockholm.
Washington says there is still no solid scientific proof that Agent Orange is responsible for numerous medical problems, including tens of thousands of birth defects.
While the case for birth defects is open, scientists have established a link between dioxin and certain cancers such as soft-tissue sarcomas and lymphomas as well as type-2 diabetes.
Nguyen Trong Nhan, head of Vietnam's Red Cross Society and the country's former health minister, said there were an estimated one million victims of Agent Orange in the country, all needing at least $1,000 in assistance.
"We don't agree with the position of the United States government to do further research on Agent Orange first and then provide assistance to the victims," he told Reuters.
Non-governmental organizations such as Oxfam also attended the Stockholm conference on the environmental legacy of the Vietnam war. Delegates also discussed unexploded ordnance and the destruction of farmland.
"Many aspects of Agent Orange problems and landmines ... can be contained or cleaned up now with adequate commitment and resources," the conference, which ended Sunday, said in its final declaration.
Not all experts and activists agreed that the United States should be blamed, but all agreed that Western aid should not wait until more studies are completed.
They said the West should provide assistance to define "hotspots" such as old military bases and airports where the planes spraying Agent Orange were loaded and other areas which still have high levels of dioxin.
The Vietnamese may yet get support from an unexpected front -- U.S. war veterans who also believe they became ill as a result of Agent Orange.
The Supreme Court is later this year to decide whether to review a lower court ruling which would give veterans a chance to sue Agent Orange manufacturers and ask for compensation.
By Anna Peltola