Some refugees escaping North Korea, including former scientists, are emerging with stories of medical and scientific experimentation on political prisoners. Human rights activists are calling on the world to pay closer attention to these stories.

The claims of experimentation on humans were relayed by an American Jewish organization best known for hunting Nazi war criminals and exposing contemporary hate groups.

Rabbi Abraham Cooper, an official of the Los Angeles-based Simon Wiesenthal Center is in the South Korean capital interviewing defectors from the communist North. He says some of them claim to have first-hand knowledge of medical and scientific experiments conducted on political prisoners.

Rabbi Cooper said in an interview that it is time for the civilized world to make sure such experiments do not continue.

"It's the kind of stories you would hear from the depths of the Soviet Gulag, from the Nazi and Japanese doctors during the course of the Second World War. This has to stop," he said. "For us to go on any further in silence is to make a mockery of the entire human rights movement."

Rabbi Cooper says two of the defectors he interviewed this week had conducted such experiments themselves, and believed their experiments were part of research into weapons of mass destruction. He said the two scientists expressed no qualms about using human subjects.

"The attitude of [the former North Korean] scientists, generally speaking, was, political prisoners were as good as dead anyway, and the notion of using them as guinea pigs for experiments that were obviously tied also to the WMD program of North Korea was really not a big deal," he said.

He went on to say that one of the defectors told him of a 1979 experiment in which two glass tanks, each holding a political prisoner, were infused with toxic gas. He was told the prisoners died.

Rabbi Cooper also said he interviewed a chemist who tested gasses on animals in North Korea. The chemist said his data was given to another group of scientists, who then conducted experiments on humans.

Rabbi Cooper detailed his claims Tuesday at a news conference in Seoul.

American officials have said they believe North Korea has chemical and biological weapons programs alongside its controversial nuclear weapons programs. Pyongyang has condemned such claims as "cheap U.S. propaganda."

The refugees interviewed by Rabbi Cooper are among hundreds of thousands who have fled repression and famine in North Korea since the mid-1990s. The famine has resulted from floods, the disappearance of aid from the former Soviet Union, and mismanagement of the North Korean economy and agriculture.

The World Food Program and the Food and Agriculture Organization said Tuesday that despite the best harvest in a decade, North Korea will need about 500,000 tons of food aid next year to feed nearly 6.5 million of its citizens most vulnerable to hunger.