"The International Peoples' Tribunal of Conscience sat on May 15-16 in Paris to hear testimony about the harmful effects of Agent Orange on Vietnam's environment and population", Thanhniemnews.com said on May 20.
The tribunal verdict said those who manufactured the chemical weapon Agent Orange and the government that authorised its use should pay full compensation to Vietnam and victims of the weapon.
Agent Orange was widely used by the US military in its war on Vietnam, which ended in 1975.
Thanhniemnews.com said 23 victims and experts addressed the tribunal, as did a delegation
representing more than three million Vietnamese victims.
The tribunal is an initiative of the International Association of Democratic Lawyers (IADL).
Thanhniewnews.com said "evidence has established that the chemical products sprayed by the US military during the Vietnam War from 1961-1971 caused damage to the people, land, water, forests, ecology, and economy of Vietnam".
"The massive spraying of Agent Orange/dioxin on the southern part of Vietnam and the massive bombardment of the northern part clearly demonstrates that the US violated the UN Charter mandate to refrain from the use of force in international relations, the tribunal said.
"The use of dioxin is a war crime because it is a chemical weapon outlawed both in customary international law and by the Hague Convention of 1907."
In 2004, Vietnamese Agent Orange victims filed a case against 37 US firms responsible for its manufacture in a New York court. However, the court ruled that the companies were not responsible for how the US government used their product.
In March, the US Supreme Court rejected a petition by the Vietnam Association For Victims of Agent Orange/Dioxin for it to hear the case.