U.S. officials have said recently that Pakistan has the fastest-growing nuclear weapons program in the world -- at least in terms of installing additional capacity to produce nuclear materials for nuclear weapons.
Now, a Washington-based think tank says it has obtained satellite imagery showing how Pakistan has concentrated in recent years on greatly expanding its nuclear-weapons-production complex.
David Albright, one of the authors of the reports by the Institute for Science and International Security (ISIS), says the expansion "has been going on for several years, but within a few years it will be finished. Most of the renovations that we've found, at least, focus on making pretty large quantities of plutonium." (Click here
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Albright says that the researchers believe that this indicates "that Pakistan wants to change the nature of its nuclear arsenal. Traditionally, it has used weapons-grade uranium as the nuclear explosive fuel. And that allowed it to build certain types of fission weapons. If they go to plutonium as the fuel for nuclear weapons, they can build smaller nuclear weapons."
Albright says Pakistan's apparent focus on plutonium is significant, both in terms of the delivery systems that could carry one of its nuclear warheads as well as the destructive power of those warheads.
"They could put them on more types of delivery vehicles -- such as cruise missiles. They could also be able to build, or try to build, thermonuclear weapons," Albright says. Qualitative Improvement
"They are pretty big, normally. And if you use plutonium in a nuclear trigger, it is an atomic bomb that sets off the thermonuclear material. Then you can get a smaller thermonuclear weapon," he continues. "And so we think the focus of Pakistan will be not just on increasing the number of its weapons, but increasing their lethality and the destructive power of those weapons."
Shannon Kile, director of the nuclear nonproliferation program at the Stockholm International Peace Research Institute, says that the ISIS's conclusions appear to be valid.
"This is pretty consistent, actually, with a number of other reports in the open-source literature, all pointing in the same direction -- which is that Pakistan is putting into place the capability to rapidly increase its production of fissile material for nuclear weapons, not only in terms of quantity but also the type of fissile material that is being produced," Kile says.
"Pakistan has relied primarily on highly enriched uranium to date. It now seems to be moving toward a plutonium-based arsenal," Kile adds. "And the reason why that is important is because plutonium weapons are, by their very nature, lighter. You can make smaller, more compact warheads which are easier to fit onto ballistic missiles."
In fact, Kile says, Pakistan has been developing its systems for delivering a nuclear warhead at the same time that it has been expanding its nuclear facilities.
"We know that Pakistan has a rather ambitious ballistic-missile and also cruise-missile development program under way with the Shaeen-2, for example -- a solid-fuel as opposed to the older liquid-fuel rockets, which not only have longer range, but are also more operationally convenient," Kile notes.
This is because they're to use "in the field" due to not having to "spend hours fueling them," Kile says, which he describes as a "qualitative improvement across the board for the Pakistan nuclear arsenal."Arsenal Under Threat?
Albright says the satellite imagery of Pakistan that he and other experts have obtained shows significant construction activities at key nuclear facilities that are known to be part of Pakistan's nuclear-weapons complex -- including nuclear reactors at Khushab, about 200 kilometers east of Islamabad; a uranium-conversion facility at Dera Ghazi Khan in southern Punjab, and Pakistan's main nuclear-weapons laboratory at Kahuta near Islamabad.
The ISIS reports also highlight cases in which gunmen have attacked the Dera Ghazi Khan nuclear site in southern Punjab. Albright points out that the attackers were "not Taliban. It was another group from Baluchistan that has grievances against the government. It exemplifies the ethnic tensions in Pakistan that are often expressed violently."
Pakistan is very sensitive to the issue of security over its nuclear arsenal and usually reacts sharply to media reports suggesting that its nuclear weapons might fall into the hands of militants or terrorists.
But Albright and Kile both conclude that the real risk is that components for nuclear weapons, or weapons-grade nuclear material, might fall into the wrong hands.
RFE/RL correspondent Heather Maher contributed to this report from Washington