A Paris court Thursday rejected an appeal by a French-Vietnamese woman who has been trying to sue Monsanto and other makers of Agent Orange for the chemical's use in the Vietnam war.

Tran To Nga, who was born in what was then French Indochina, accused 14 agrochemicals firms of causing grievous harm to her and others by selling Agent Orange to the American military, which used the herbicide to devastating effect in Vietnam.

She lost her initial case in 2021, when a French court ruled that the companies enjoyed legal immunity from prosecution because they worked for a sovereign government.

The Paris Court of Appeal used the same argument in rejecting Nga's claim.

Her demands "come up against the companies' immunity status," the court said in its written ruling, seen by AFP.

Nga will now take her case to France's highest appeals court for a final ruling, her lawyers said.

The 82-year-old, who covered the 1955-1975 war as a reporter and has lived in France for the past three decades, also accused the companies of environmental damage.

Campaign groups estimate that four million people in Vietnam, Laos and Cambodia were exposed to the 76 million litres (20 million gallons) of Agent Orange sprayed by US forces to destroy ground cover and food sources in its battle with communist North Vietnamese troops between 1962 and 1971.