'Satellite photos of Pakistan's Khushab nuclear site show what appears to be a partially completed heavy-water reactor capable of producing enough plutonium for 40 to 50 nuclear weapons a year, a 20-fold increase from Pakistan's current capabilities, according to a technical assessment by Washington-based nuclear experts,' says the Post article.

The site is adjacent to Pakistan's only plutonium production reactor, 'a modest, 50-megawatt unit that began operating in 1998. By contrast, the dimensions of the new reactor suggest a capacity of 1,000 megawatts or more, according to the analysis by the Institute for Science and International Security, (ISIS). Pakistan is believed to have 30 to 50 uranium warheads, which tend to be heavier and more difficult than plutonium warheads to mount on missiles,' says the Post.

"South Asia may be heading for a nuclear arms race that could lead to arsenals growing into the hundreds of nuclear weapons, or at minimum, vastly expanded stockpiles of military fissile material," the Institute's David Albright and Paul Brannan concluded in the technical assessment, a copy of which was provided to The Washington Post.

'Such a reactor could produce over 200 kilograms of weapon-grade plutonium per year, assuming it operates at full power for a modest 220 days per year. At 4-5 kilograms of plutonium per weapon, this stock would allow the production of over 40-50 nuclear weapons a year. The reactor could also be used to produce substantial amounts of tritium for boosted fission weapons,' says the ISIS report.

Two other independent nuclear experts endorsed the assessment after reviewing the commercially available satellite images, provided by Digital Globe, and supporting data, the Post said.

While Pakistani officials declined comment, a senior Pakistani official, speaking on condition of anonymity, acknowledged to the Post that a nuclear expansion was underway. "Pakistan's nuclear program has matured. We're now consolidating the program with further expansions," the official told the Post. These include "some civilian nuclear power and some military components."

The report comes as Congress prepares to debate the controversial India-US civilian nuclear cooperation agreement, which would grant India access to sensitive US nuclear technology in return for placing its civilian nuclear reactors under tighter safeguards.

Acccording to the Post, 'India currently has an estimated 30 to 35 nuclear warheads based on a sophisticated plutonium design. Pakistan, which uses a simpler, uranium-based warhead design, has sought for years to modernize its arsenal, and a new heavy-water reactor could allow it to do so, weapons experts say.'

"With plutonium bombs, Pakistan can fully join the nuclear club," the article quoted a Europe-based diplomat and nuclear expert who requested that he not be named.

According to the Post, 'there was no immediate reaction to the report from the Bush administration. Albright said he shared his data with government nuclear analysts, who did not dispute his conclusions and appeared to already know about the new reactor.'

"If there's an increasing risk of an arms race in South Asia, why hasn't this already been introduced into the debate?" asked Albright.