U.S. President George W. Bush underscored some of those threats in a major policy speech two weeks ago. Bush described how a secret network centered on Pakistani scientist A.Q. Khan conducted a profitable trade in nuclear secrets for decades. And he warned that nuclear weapons are becoming easier to acquire, both for states and terrorist groups.
"These terrible weapons are becoming easier to acquire, build, hide, and transport. Armed with a single vial of a biological agent or a single nuclear weapon, small groups of fanatics, or failing states, could gain the power to threaten great nations, threaten the world peace," Bush said.
France, among other countries, is also stressing the danger of proliferation. French Foreign Minister Dominique de Villepin this month called proliferation a major threat to international stability.
"The proliferation of weapons of mass destruction constitutes another major threat to international stability. It increases the risk of crisis in the most sensitive regions of the world. It threatens to considerably increase the power of destruction from terrorist groups who, we know, are seeking to access these weapons," de Villepin said.
The warnings come as Iran and Libya are being intensively investigated by the UN nuclear agency for buying nuclear designs or parts on the black market. Libya recently renounced its nuclear weapons development effort, while Iran maintains that its nuclear program is for peaceful energy purposes only.
Iran's Foreign Ministry spokesman Hamid Reza Assefi acknowledged this week that Tehran has obtained nuclear components from what he called "dealers," but did not elaborate.
"We have acquired some components from some dealers. About the exact material, what was that, I don't know. I'm not in a position, unfortunately, to give you any more information," Assefi said.
The UN's International Atomic Energy Agency this week urged Iran to be "much more prompt" in declaring all its nuclear activities and procurement sources as part of its deal with the agency to prove it has no clandestine weapons programs.
But if the ability of countries like Libya and Iran to get nuclear technology through the black market is increasingly worrisome, nuclear experts say cracking down on private proliferators will not be easy.
Corey Hinderstein, a nuclear nonproliferation analyst at the Institute for Science and International Security (ISIS) in Washington, D.C., says the black marketeers are adept at providing customers with weapons-related technology from businesses that appear unconnected with the nuclear sector.
"I think there is a misperception about the kind of technology that is being spread around the world, in that it is not nuclear technology. This is what we would call dual-use technology. And whereas nuclear industries are very highly regulated and monitored, high-tech manufacturing is not. And that's the kind of specific industry that we are looking at," Hinderstein said.
As one example, she cites an ongoing investigation into evidence the trafficking network made use of a factory in Malaysia to produce nuclear components for Libya.
"The company in Malaysia, they are a precision engineering group which has experience in machining of components to very high specifications. But there is nothing about that skill that is related to the nuclear industry, and they were exploited because they have this skill and were willing to do something without asking a whole lot of questions," Hinderstein said.
The nuclear expert says one thing that is needed to crack down on nuclear trafficking is to tighten export controls worldwide. She says that today, states are free to choose for themselves what export controls they want to impose on their industries and what sort of penalties to levy on abusers.
"Something that would help tremendously would be, on a global scale, something like a new treaty, where states are required to control the technology that is coming out of their citizens and their industry, and there are actual repercussions not just for the individuals and companies but for the states involved if they fail to enforce their own laws or international law," Hinderstein said.
Nuclear experts recognize that getting states worldwide to agree on collective responses to threats is never easy. But they warn that without such tough new measures, the danger posed by the global black market in nuclear-related material and equipment is only likely to grow.
Click here to read Part 1 of this series on the global black market in nuclear technology.