Islamabad evidently is increasing its capabilities in response to the likelihood that New Delhi would forcefully respond to another large-scale terrorist attack perpetrated by Pakistani-based extremists.

"A [Hatf 9] would have to drive all the way up to the Indian border to be able to reach important targets in India," Kristensen said. "Amritsar would be one candidate, as would several smaller cities along the border. But that would also expose the missile to counterattack."

The Pakistani army previously said the Hatf 9 "could carry nuclear warheads of appropriate yield with high accuracy" and possesses the ability to be quickly relocated following use.

Kristensen said the time had come for Islamabad to provide information on the size, scope, and intent of its nuclear arsenal.

Though Pakistan is widely seen to have the world's fastest-growing deterrent, speculation that the state would overtake France as the planet's fourth-largest nuclear weapons state is "a decade or two ahead," Kristensen said.

"Pakistan's nuclear arsenal is not equal to the number of warheads that could potentially be produced by all the highly enriched uranium and plutonium Pakistan might have produced. The size also depends on other factors such as the number of delivery vehicles and other limitations," he said.

Concerns about Pakistani nuclear security led France in 2009 to choose not to export atomic power technology to the energy-hungry country, the Press Trust of India reported on Sunday. French presidential diplomatic adviser Jean-David Levitte informed U.S. diplomats that Paris was "not sure that the Pakistani nuclear deterrent is secure," particularly given "the frequent movement of nuclear weapons by the Pakistani military," according to a September 3, 2009, U.S. cable made public by the transparency group WikiLeaks.

French Defense Minister Gerard Longuet, speaking in New Delhi last week, voiced his worries about India's nuclear-armed rival: "This part of the world needs some clarification and stability as well. India is an old strategic partner.... Regarding Pakistan we are waiting for clarifications." International concerns about the security of Pakistan's nuclear weapons were renewed by incidents that called into question the military's competence -- the news that al-Qaeda chief Osama bin Laden was able to escape detection for years in the country and a 17-hour siege on a naval base in Karachi last week by a handful of militants.

There are a number of scenarios in which Pakistani nuclear weapons might be placed at risk for diversion to rogue actors, according to Reuters.

Islamabad generally keeps its nuclear warheads apart from their carriers, but they could be combined and fielded in the event of conflict with India. Authentication codes would still be required to fire weapons such as the Hatf 9, said Shaun Gregory, director of the Pakistan Security Research Unit at the University of Bradford in the United Kingdom.