The US military used Agent Orange, named after its orange-striped containers, to defoliate areas believed to be harbouring opposing forces.

It contained dioxin, a chemical linked to a variety of diseases and which Vietnam has blamed for a spate of birth deformities.

Vietnamese victims' groups say the US military sprayed about 80 million litres (21 million gallons) of herbicides, much of it Agent Orange, over southern Vietnam during a 10-year period.

But there has been no internationally-accepted scientific study establishing a link between Agent Orange and Vietnam's disabled and deformed, a US embassy spokeswoman in Hanoi said.

Hoang Van Hue helps his dribbling 31-year-old son sit back in his rusting wheelchair. His daughter, 26, hunches over in her own wheelchair, sticking her fingers in her mouth to make a blowing noise.

"I think that my children were affected with Agent Orange from me," their father said.

The former Vietnamese infantryman said he was exposed to the herbicide dropped by American troops during the war which ended in 1975.

Hue and other Vietnamese who say they are victims of the toxin want the United States to compensate them for its wartime "mistake," and vow to press their claim despite a US Supreme Court decision in March.

The top court declined to hear the victims' appeal after a US district court in 2005 dismissed their lawsuit against manufacturers of the herbicides.

"We are angry but we stay calm and will continue our fight," says Nguyen Trong Nhan, vice president of the Vietnam Association for Victims of Agent Orange/Dioxin, which he says represents about three million victims, and was a plaintiff in the lawsuit.