Jimmy Carter, Mikhail Gorbachev, the American Medical Association and 48 nations are among those lobbying the Supreme Court (search) to end the execution of killers who committed their crimes before age 18.

The United States is among only a handful of nations that allow the practice. The high court will reconsider this fall whether such executions are constitutional.

A collection of death penalty opponents on Monday planned to challenge the practice.

"By continuing to execute child offenders in violation of international norms, the United States is not just leaving itself open to charges of hypocrisy, but is also endangering the rights of many around the world," said the filing on behalf of Nobel Peace Prize winners, including former President Carter and former Soviet President Gorbachev.

"Countries whose human rights records are criticized by the United States have no incentive to improve their records when the United States fails to meet the most fundamental, baseline standards," it said.

The 25-nation European Union, plus Mexico, Canada and other nations argued that execution of juvenile killers "violates widely accepted human rights norms and the minimum standards of human rights set forth by the United Nations."

Mexico noted separately that three of the 73 current death row inmates condemned for killings that took place before they were 18 are Mexican nationals.

The American Medical Association (search), American Psychiatric Association (search) and other medical and mental health groups also told the court they oppose execution of teen killers, as did the U.S. Conference of Catholic Bishops (search).

Diplomats including former undersecretary of state Thomas Pickering and former ambassador to France Felix Rohatyn argued that growing international consensus against such executions leaves the U.S. diplomatically isolated.

The United States executed more young killers than the rest of the world combined between 1990 and 2003, the diplomats' filing said.

In the past four years, only five nations have executed juveniles, the diplomats said: Congo, China, Iran, Pakistan and the United States.

"In no other area of human rights does the United States consider these nations to be our equals," the filing said.

Two friend-of-the-court briefs filed earlier support continuation of the practice.

"(Our) experience strongly indicates that a bright-line rule categorically exempting 16- and 17-year-olds from the death penalty — no matter how elaborate the plot, how sinister the killing, or how sophisticated the cover up — would be arbitrary at best and downright perverse at worst," lawyers for Alabama, Delaware, Oklahoma, Texas, Utah and Virginia told the court.

Those states are among 19 that allow execution of killers who were 16 or 17 at the time of the crime. Not all states that allow the death penalty apply it to underage killers, and no state allows the execution of those who were younger than 16 at the time of the crime.

The Supreme Court has agreed to hear a case from Missouri, where the state Supreme Court declared juvenile executions unconstitutional last year.

Christopher Simmons was 17 when he and an accomplice broke into the Fenton, Mo., home of Shirley Crook in 1993, then bound her with tape, electrical wire and the belt from her bathrobe and pushed her off a railroad bridge to drown.

Prosecutors said Simmons told teenage friends that they would get away with it because of their ages.

The liberal wing of the nine-justice Supreme Court is already on record supporting 18 as the minimum age of eligibility for the death penalty. Those four justices took an extraordinary step in the fall of 2002, signing a dissent in an appeal by a death row inmate that called it "shameful" to execute juvenile killers.

"The practice of executing such offenders is a relic of the past and is inconsistent with evolving standards of decency in a civilized society," Justice John Paul Stevens wrote then. He was joined by Justices David H. Souter, Ruth Bader Ginsburg and Stephen Breyer.

The issue turns on the Constitution's ban on "cruel and unusual punishments," and is similar in many ways to the question of whether mentally retarded killers can be executed for their crime. The Supreme Court banned that practice in 2002.

The Case is Roper v. Simmons, 03-633.