UNITED NATIONS — A new international convention is needed to prevent trafficking in kidneys and other organs and potentially life-saving tissues and cells, according to a joint study by the United Nations and the Council of Europe released Tuesday.

The study calls for international experts to agree on a definition that is recognized worldwide of what constitutes "trafficking in organs, tissues and cells."

Carmen Prior, the public prosecutor of Austria and a co-author of the study, said the definition should be incorporated into an international convention that would include measures to prevent the crime, to protect and assist donors, and to prosecute the traffickers — "especially intermediaries and brokers and doctors and medical staff involved in such activities."

The study stressed that trafficking in human beings for the purpose of removing an organ is a small part of the wider problem of organ trafficking.

It said exploiting a living person to get an organ is already a crime under a U.N. protocol and a Council of Europe convention against human trafficking, but there is currently no international legal instrument against trafficking in organs, tissues and cells.

Arthur Caplan, a co-author of the study who chairs the University of Pennsylvania's Department of Medical Ethics and directs its Center for Bioethics, said the report reinforces the belief by many "that the basis for obtaining organs and tissues for transplant should be voluntary altruism."

He told a news conference launching the report that it reaffirms "as a primary principal" that there should be no financial gain involved in obtaining organs and tissues for transplant.

All national and international laws should incorporate this principal and prohibit the sale or payment for organs, Caplan said.

"The problem that leads to trafficking is basically shortage," he said.

"The good news is many nations are starting to take steps to reduce or attack the problem of trafficking of organs," Caplan said.

In August, for example, China's state media reported that the majority of transplanted organs in the country come from executed prisoners, a rare disclosure about an industry often criticized for being opaque and unethical.

At the same time, the country's Health Ministry and the Red Cross Society of China launched a national organ donation system to reduce the reliance on death row inmates and encourage donations from the public.

The U.N. and Council of Europe study calls for the promotion of organ donations, preferably from those who have died, stepped up efforts to train surgeons in all countries to transplant organs, and better data on the scale of trafficking in organs, tissues and cells — and on men and women trafficked to obtain an organ.

The study was the brainchild of U.N. Assistant Secretary-General Rachel Mayanja, the secretary-general's special adviser on gender issues and the advancement of women, and the Council of Europe's Deputy Secretary-General Maud de Boer-Buqicchio.

Mayanja expressed hope that the U.N. General Assembly, which would have to draft and approve a new convention, would put the issue of organ trafficking on its agenda and start debating the issue.

"We would like, of course, to see work on a convention, a binding convention, start as soon as possible," she said.