Pakistani Prime Minister Nawaz Sharif is expected to strongly resist any limits on Pakistan's use of small tactical nuclear weapons at a meeting with U.S. President Barack Obama.
Pakistan insists smaller weapons have deterred an attack by its rival and neighbor, India, which is also a nuclear power.
But the United States worries tactical weapons are further destabilizing an already volatile region because their smaller size makes them more tempting to use in a war and they might be easier for militants to obtain.
Sharif and Obama will meet at the White House on October 22, with the United States pushing for a commitment from Pakistan to not develop and use nuclear weapons that in some cases Western analysts fear are as small and portable as shoulder-launched rockets.
But Pakistani officials see the White House demands as unreasonable, especially because it is not offering much in return apart from a vague promise to formally recognize Pakistan's nuclear capabilities.
"Our nuclear program is one-dimensional: stopping Indian aggression before it happens. It is not for starting a war. It is for deterrence," Pakistani Foreign Secretary Aizaz Chaudhry told a briefing on October 20.
Chaudhry explained that Pakistan's arsenal of tactical weapons makes it difficult for India to consider launching a strike in Pakistan's territory -- to pursue suspected terrorists, for example -- with the thought that it can prevent the conflict from turning from conventional to nuclear.
Pakistan's recent testing of very short-range and small nuclear missiles that it could use in a war with India was, in fact, a reaction to Indian threats to make a limited, lightning raid with conventional forces in case of militant attack, he said. The Indian strategy is known as the "Cold Start" doctrine.
"In India, they brought the Cold Start doctrine," Chaudhry said. "So we have also preserved our deterrence capability."
As to the White House's hope of securing curbs on Pakistan's nuclear arms, Chaudhry was adamant that wouldn't happen.
"We are not signing a nuclear deal. No deal, not of any kind."
To the contrary, Pakistan seems intent on expanding its nuclear arsenal and is working on a nuclear submarine, one official told Reuters.
"The goal is a sea-based second strike capability," the official said, referring to a submarine that could carry nuclear warheads and strike in case land-based nuclear weapons were wiped out.
U.S. Secretary of State John Kerry met with Sharif on October 21 but State Department spokesman John Kirby declined to say whether a U.S. call for nuclear restraint was discussed.
Kirby told a regular news briefing Pakistan remained engaged with the international community on nuclear security and added, "We believe that they believe in the importance of nuclear security issues."
Kirby also said the United States encouraged India and Pakistan to engage in direct dialogue to reduce tensions.
"The normalization of relations between Pakistan and India is vital to both countries and to the region," he said, while adding Kerry and Sharif discussed the need for more efforts against militants in Pakistan.
Pakistan and India have fought three wars since becoming separate countries in 1947. Both claim the disputed Himalayan region of Kashmir. India frequently accuses Pakistan of supporting militants operating on Indian territory.
While Pakistani officials insist that their nuclear arsenal is an effective deterrent that has prevented all-out war with India, nonproliferation experts worry that Pakistan's tactical weapons actually increase the risk of nuclear conflict.
"The smaller they are, the more tempting it becomes to use them against a conventional force," nuclear physics professor Pervez Hoodbhoy says.
"The development and deployment of tactical nuclear weapons is a complete change of strategy. Earlier, nuclear weapons were instruments for deterring war, but now they're seen as weapons for actually fighting a war."
India has said that any nuclear attack on its forces would be treated as a nuclear strike on India itself and it would respond accordingly.
So observers warn any use of even small weapons by Pakistan could quickly escalate into a full-blown nuclear conflict.
