Bowing in part to world opinion, the US Supreme Court on Tuesday abolished the juvenile death penalty in a ruling that immediately sparked controversy over whether the justices should listen to the views of foreign countries when interpreting the US constitution.

The 5 to 4 ruling, a big victory for death penalty opponents, brought America into line with the rest of the world where execution of juveniles is almost unheard of. The ruling will save the life of a 17-year-old who robbed a woman, wrapped her head in duct tape and threw her off a railroad bridge while still alive. It could also affect about 70 other death row inmates who were 16 or 17 when they committed their crimes.

The ruling also highlighted the unpredictable politics of a court that is widely viewed as overwhelmingly conservative, but has issued surprisingly liberal rulings on social issues in recent years.

Writing for the five-person majority, Justice Anthony Kennedy argued that a national consensus has emerged against juvenile execution since the court last visited the issue 15 years ago. "Today society views juveniles.as 'categorically less culpable than the average criminal,'" he wrote, echoing an earlier ruling against the execution of the mentally retarded. "Neither retribution not deterrence provides adequate justification for imposing the death penalty on juvenile offenders," he wrote.

He acknowledged the important -- and controversial -- role international opinion played in the decision. "The overwhelming weight of international opinion against the juvenile death penalty is not controlling here but provides respected and significant confirmation" of the ruling, he wrote.

But his reliance on international opinion sparked an angry dissent read from the bench by Justice Antonin Scalia, who argues that modern foreign law should not be used to interpret the constitution. Arguments over the role of foreign law have broken out more and more frequently, as globalisation has led to increasing numbers of cross-border disputes, and as several of the justices have begun to look overseas in defending their rulings.

Justice Scalia instisted on Tuesday that it was premature to declare a national consensus in favour of abolishing the death penalty, and accused the majority of substituting its own moral judgment for true social consensus.

"Though the views of our own citizens are essentially irrelevant to the court's decision today, the views of other countries and the so-called international community take centre stage," he complained. "The basic premise of the court's argument - that American law should conform to the laws of the rest of the world - ought to be rejected out of hand," he said.

Three other justices also dissented, including William Rehnquist, Chief Justice, and Sandra Day O'Connor - highlighting the fact that replacing one or more conservative justices - notably Justices Rehnquist and O'Connor, rumoured to be the most likely to depart - would not necessarily change the court's rulings, especially on such social issues.