One of the key issues likely to come up during President Bill Clinton's visit to Vietnam this week is the legacy of Agent Orange, the toxic defoliant used by US forces which has been blamed for huge numbers of birth defects.

Agent Orange was used to destroy tree cover

The Vietnamese authorities say they fear that illnesses caused by Agent Orange are now being passed on to a third generation of victims.

During the war in Vietnam the Americans sprayed millions of gallons of Agent Orange on the country in an attempt to deny food and cover to the enemy.

To Tien Hoa is a 65 year old grandfather who spent seven years fighting against the Americans.

He was repeatedly sprayed by agent orange. "My son was born with a deformed foot and now my grandson has no legs and a deformed hand. I can confirm this is because of Agent Orange."

This girl's skin is covered in black spongy blotches

Scientists say it is not that simple. The US does pay compensation to some of its own serviceman for Agent Orange related illnesses, but proving a link between various medical conditions and Agent Orange is difficult and highly controversial.

There is, however, widespread agreement the dioxin which Agent Orange contained is very dangerous.

Some parts of Vietnam, especially the sites of former US air bases where the herbicide was stored, have high concentrations of dioxin.

The US sprayed 20 million gallons over Vietnam

The most thorough survey yet has been conducted by a Canadian, Chris Hatfield, who says that in some places it appears dioxin has not really reduced at all.

"Dioxin has moved from the soils to the sediment of fish ponds and into the fish themselves that are raised in the ponds for food - right up into the blood and breast milk," he added.

Clean-up

This child was born with no legs

The suspicion that 25 years after the war, dioxins could still be infecting foetuses through the placenta and infants through breast milk has added urgency to the demands for a clean up.

"So far the Vietnamese government has not been able to do anything to clean up," said Professor Le Cao Dai, the Executive Director of the Agent Orange Victim Fund and one of Vietnam's leading experts on the issue.

To break down dioxin, affected soil has to be heated to very high temperatures - an expensive process.

Many handicapped come from villages that were sprayed

President Clinton is expected to stress the US's commitment to international research on the issue.

In recent months the US has also, for the first time, begun to discuss the possibility of providing technical assistance for a clean-up of Agent Orange.

Pete Peterson, the US ambassador in Vietnam and a former prisoner of war during the conflict, says they are beginning a "full research effort on Agent Orange".