News media in Northeast Asia are reporting details of alleged cooperation between Iran and North Korea in trying to build atomic bombs. Such joint activities have been suspected for years.
South Korea?s foreign ministry and the national intelligence service say they cannot comment on fresh reports linking Pyongyang's atomic efforts to Iran.
Officials with the agencies considered at the forefront of monitoring North Korea's nuclear programs say the allegations, apparently leaked by diplomats in recent days, involve classified information.
The allegations follow last Tuesday?s report by the International Atomic Energy Agency, the U.N.?s nuclear watchdog.
The IAEA's most comprehensive assessment yet about Iran's nuclear programs details what it says is evidence of Iran's covert and continuous effort, since 2003, to build a nuclear bomb, going far beyond the stated goals of energy and medical research.
Last Friday, Iran's top envoy to the IAEA, Ali Asghar Soltanieh, called the report a fabrication based on "lousy" intelligence by the United States and its allies.
The 25-page report has since been leaked and makes no mention of a link between Iran and North Korea. But last Friday U.N. investigators gave a private technical presentation to the 35 member states of the IAEA Board of Governors. Since then, diplomats have been quoted anonymously by South Korea media alleging that hundreds of North Korean scientists and engineers have been working at nuclear and missile facilities in Iran.
Japanese newspaper Sankei Shimbun says among the Iranian sites the North Koreans have been visiting are three research centers carrying out simulations of how to trigger nuclear weapons.
Bruce Bennett, a senior defense analyst at the Rand Corporation, which conducts research and analysis for the U.S. military and intelligence agencies, says experts, for years, have been suspicious about this type of cooperation.
"There've been stories of Iranians at the nuclear tests in North Korea, for example," Bennett said. "So if information is really being shared then you've got a much more dangerous situation because most people would argue that the North Korean nuclear program is out ahead of Iran and we don't want Iran having that assistance."
The London-based International Institute of Strategic Studies, in a report this year, characterized the cooperation as mutual. It said North Korea has a technological edge over Iran in uranium enrichment and the manufacture of nuclear-related equipment, such as high-strength steel. The IISS report said North Korea's weapons programs also benefit from Iranian technology.
Bennett, of the Rand Corporation, says the international community needs to pay more attention to the nuclear links between North Korea and Iran.
"But stopping that or even slowing it down is going to be complicated. The people can travel to Iran without having to go through places where we can't stop them," he said.
The South Korean media reports say the North Koreans enter Iran covertly through other countries, such as Russia and China. The North Koreans are said to be employed at 10 nuclear and missile facilities in Iran and are apparently rotated every few months.
The Washington Post reported November 7 that Western diplomats and nuclear experts briefed on the IAEA findings say that Iran has reached the threshold of nuclear capability with crucial technology linked to North Korea and Pakistan.
Iran and North Korea were customers of the network run by Pakistani nuclear scientist A.Q. Khan. And both countries are under United Nations economic sanctions for their nuclear programs.
U.S. President Barack Obama, at the conclusion of Sunday's APEC Summit in Hawaii, told reporters the sanctions against Tehran have had "enormous bite" and he will consult with other nations about additional steps to prevent Iran for acquiring an atomic weapon.
North Korea has also been accused in U.N. and other reports of possibly supplying not only Iran but also Syria and Burma with banned atomic technology.
In August, German newspaper Sueddeutsche Zeitung reported North Korea had provided Iran with a computer program that can help scientists identify self-sustaining chain reactions, vital for the construction of reactors and also in the development of nuclear explosives.
Analysts say they have also been tracking, since the 1980s, cooperation between Pyongyang and Tehran on missile development.
Of utmost concern is whether North Korea has given Iran some Russian designed advanced missiles. There is no evidence, however, that either North Korea or Iran has flight-tested the missile, known as the BM-25 or Musudan.
Russia denies its existence. Some analysts contend previous public displays of the Musudan in Pyongayng military parades were merely fakes. The missile is believed to be based on the former Soviet Union?s R-27, a submarine-launched missile with a range of between 2,500 and 4,000 kilometers, designed to carry nuclear warheads.
In a presentation at a think tank seminar in Seoul last week, Bennett of the Rand Corporation, said there is wide speculation about the size of North Korea's possible nuclear weapons arsenal. He said Pyongyang may not have any weapons yet but could have "as many as 20" with the number of reliable ones ranging between two and 16.
But Bennett is adamant that it would be wrong to characterize North Korea as a nuclear power because it has not demonstrated a working atomic bomb, despite carrying out tests of nuclear devices in 2006 and 2009.
The two Koreas have no diplomatic relations. They fought a three-year civil war to a stalemate in the early 1950's. They technically remain at war as no peace treaty has ever been signed.