The Supreme Court let stand on Monday the dismissal of lawsuits by Vietnamese nationals and U.S. military veterans against Dow Chemical Co, Monsanto Co and other chemical makers over the use of the herbicide Agent Orange during the Vietnam War.

Without comment, the justices declined to review a ruling last year by a U.S. appeals court in New York that the plaintiffs could not pursue their claims for their alleged injuries from their exposure to the chemical defoliant.

In one case, the Vietnamese nationals said the companies should be held liable for supplying the U.S. military with Agent Orange for spraying in areas of South Vietnam in the 1960s, in violation of international law.

The plaintiffs had sought class-action status for millions of Vietnamese people. The appeals court upheld a federal judge's ruling that Agent Orange had been used as a defoliant, not as a poison designed for or targeting human populations.

In a second case, U.S. military veterans or their relatives said a federal judge and the appeals court had erred in ruling the companies could assert a government-contractor defense that shields them from liability.

In 1984, seven chemical companies, including Dow and Monsanto, agreed to a $180 million settlement with U.S. veterans who claimed Agent Orange had caused health problems.