SINGAPORE Pakistan's successful test of a missile able to carry short range nuclear weapons threatens to raise tensions in a region already nervous that the death of Osama bin Laden will create more instability.
Tactical nuclear weapons, as these are called, are often seen as more dangerous than the traditional strategic weapons because their small size and vulnerability to misuse. Theft makes them a risk to global security.
The biggest concern is that these low yield weapons are seen as less destructive and therefore more likely to be used than other classes of weapons, forcing most nuclear states to minimise the risk by cutting back stockpiles.
Pakistani experts say the country has been forced to develop tactical nuclear weapons because of India's "Cold Start" plan under which Indian troops are primed to carry out a lightning strike inside Pakistan if another Mumbai-style attack is traced back to Pakistan-based militant groups.
The military said it had tested last month the 60-km (36-mile) range NASR surface-to-surface missile which carries nuclear warheads to boost "deterrence at short ranges".
Security experts in the United States, India and Pakistan said it meant the military planned to deploy these weapons in the battlefield, escalating the regional nuclear competition that has often seemed a replay of the U.S.-Soviet rivalry during the Cold War.
"Pakistan's development and testing of nuclear-capable short-range missiles is a destabilizing and potentially dangerous development," Daryl G. Kimball, the executive director of the Washington-based Arms Control Association, said.
"It suggests that Pakistan would seriously contemplate use on the battlefield in the event of an incursion by Indian forces."
India may yet respond by mounting nuclear warheads on its shorter range missiles to meet the Pakistani threat. It tested low yield nuclear devices in 1998 but there has been no word since then on whether it has added them to its arsenal.
"Our capability in the area of low yield fission devices is well known," a former Indian defence scientist involved in the 1998 tests said, declining further comment.
Pakistan responded to India's tests with explosions of its own. Both nations have since been expanding their arsenal, Pakistan even more and at a pace that Western experts say may, within a decade, make it the fourth largest weapons power, behind the United States, Russia and China.
Pakistan says it has invested a lot of resources to ensure that its nuclear facilities, materials and weapons are secure.
But Pakistan's support for militant groups including al Qaeda and the Taliban, who have found sanctuary along the Afghan border, has always heightened concerns about its ever expanding armoury. These worries have deepened after al Qaeda leader bin Laden was found and killed in a garrison town.
If there was one nuclear-armed country that kept him awake at night, it was Pakistan, senior White House coordinator on weapons of mass destruction and terrorism, Gary Samore said.
"What I worry about is that, in the broader tensions and problems within Pakistani society and polity...even the best nuclear security measures might break down," Samore said in an interview published in the May 2011 issue of Arms Control Today.
"You're dealing with a country that is under tremendous stress internally and externally, and that's what makes me worry."
The problem with deploying tactical weapons to the battlefield is that command and control has to be dispersed down to military units on the ground.
This increases the risk of things going wrong, either through miscalculation, an accident or the nightmare scenario of infiltration by militant groups, nuclear experts say.
In either case, once Pakistan had fired off the missile, it would invite retaliation, the extent of which is unknown.
Within Pakistan itself, security experts have questioned the logic of deploying tactical weapons, arguing that it exposed the country to bigger risks rather than improving security.
Ejaz Haider, a Pakistani security expert and columnist, said if Pakistan is going to unleash these weapons as the Indian military crosses the border, it would effectively be dropping them on its own soil.
"We are, of course, not even considering how our own troops and population would be exposed to the fallout from a TNW (tactical nuclear weapon)," Haider said.
But several experts also say that India's Cold Start doctrine, even if it is not fully operational, is seen as a real threat in Pakistan.
Cold Start is aimed at mounting rapid military incursions into Pakistan to punish it, take limited amounts of territory, and then negotiate to compel Islamabad to rein in militant groups that act against India.
It is not aimed at threatening the Pakistani state into resorting to its final, nuclear option, but it's a risky gamble. Pakistani army chief General Ashfaq Kayani has warned the Indian battle plan could lead to a "sudden spiral escalation".
"India's military planners foolishly believe that they can engage in and win a limited conventional conflict without triggering a nuclear exchange even though the Pakistani army's strategy lies on nuclear weapons to offset India's overwhelming conventional superiority," the Arms Control Association's Kimball said.
(Editing by Miral Fahmy)