Opponents of the death penalty suffered a setback at the U.S. Supreme Court Monday. The high court has refused to consider banning the executions of murderers who were younger than 18 at the time they committed their crimes.

Four of the nine Supreme Court justices wanted the high court to continue its examination of the death penalty by considering an end to the execution of murderers who committed their crimes as juveniles.

Writing for the liberal minority on the court, Justice John Paul Stevens said the practice of executing young offenders is "a relic of the past." He urged his colleagues to put an end "this shameful practice."

But the five member conservative majority on the court disagreed with that view, which means the court will not deal with the issue of juvenile executions during its current term.

The ruling comes as a disappointment to anti-death penalty activists who believe public opinion is shifting in their favor. William Schultz is Executive Director of Amnesty International USA. He notes that the United States is among only a handful of countries that permit the execution of juvenile killers.

"Our laws declare that a person under 18 is too young and irresponsible to carry out the most fundamental obligations of a citizen, but not too young to be held fully responsible as an adult for a crime," he said. "Where is the logic in that?"

Supporters of a ban on executing juveniles were hoping to build on a ruling earlier this year in which the Supreme Court banned the execution of mentally-retarded criminals, a move hailed by human rights activists.

Nevertheless, public support for the death penalty in the United States has remained fairly strong in recent years, in part because of the efforts of victims rights groups.

Dudley Sharp is with a group based in Houston called Justice for All. "My belief is that the foundation for the death penalty is what it always has been, and that is that under certain circumstances, it is considered just," he said.

At the moment, 16 of the 38 states that allow the death penalty prohibit it for those under the age of 18.