Pakistan has disclosed for the first time that it has made low-yield nuclear weapons for use in the event of a sudden attack by its larger neighbour and rival, India.
Pakistan has had nuclear weapons for years but this is thought to be the first time it has spoken publicly about its nuclear arsenal.
The disclosure was made by Pakistan's Foreign Secretary Aizaz Chaudhry during a news briefing in Washington on Monday.
It comes before Pakistani Prime Minister Nawaz Sharif is to meet Barack Obama in Washington on Thursday.
The two are expected to discuss Pakistan's nuclear programme among other issues, including Afghanistan and militant groups such as the Haqqani network and Lashkar-e-Taiba.
Mr Chaudhry's disclosure is seen by many as the first concrete explanation by a Pakistani official of how Pakistan intends to deal with possible Indian aggression.
Is it a surprise?
"The fact that Pakistan was making small tactical nuclear weapons was clear to the world from the day Pakistan started its missile programme," says Pervez Hoodbhoy, a nuclear physicist and independent security analyst based in Lahore.
"It meant that Pakistan had developed low-yield nuclear warheads to be delivered by those missiles at short ranges, in a battlefield, having localised impact, unlike big bombs designed to destroy cities."
Experts believe that the 2011 testing of the nuclear-capable Nasr missile with a 60km range was an indication that Pakistan was building an arsenal of tactical nuclear weapons for use in a theatre of war.
Hasan Askari Rizvi, a Lahore-based expert on defence and security issues, suspects Pakistan may have designed even smaller nuclear weapons, capable of being shot from a specially-designed gun.
"The Americans apparently know about these weapons, and recent debate in the US media suggests that Pakistan may actually be in possession of tactical weapons which are greater in number and accuracy than those of India," he says.
How worried should we be?
Mr Hoodbhoy points out that these battlefield weapons could be more dangerous than larger weapons because in the event of a conflict, they will need to be spread out, deployed at multiple locations closer to the targets, and would need to be fired at short notice.
"Compliance with nuclear command and control procedures may not always be adequately ensured for all the missile units deployed across a theatre," he says.
Another matter of concern for Western powers is the fact that Pakistan developed these weapons despite nuclear-related international sanctions in force since 1998, when it carried out its first nuclear test.
There is a belief that much of this technology has been acquired from China, a pipeline which will be difficult to block unless Pakistan is brought into the nuclear mainstream.
What's the US doing?
There have been suggestions the US may offer Pakistan membership of the Nuclear Suppliers' Group, with legitimate access to available research and technology, in return for some curbs on fissile material production and its missiles programme.
In Pakistan, where the civilian leadership has seemingly been under pressure from the military in matters related to defence and foreign affairs, these suggestions are being touted as a warning that the Americans might try to force Mr Sharif, a civilian, to agree to nuclear curbs.
What prompted the Pakistani move?
Mr Chaudhry's statement came against this backdrop, and since he has made no significant disclosures, Prof Askari thinks there may be two reasons why he chose to talk about the issue at all.
"One is apparently to reassure domestic audience that there's going to be no 'sell-out' on the nuclear issue," he says.
"The second may well be to officially confirm to India what it might expect if it ever decides on surgical action or hot pursuit inside Pakistan."
Pakistan banned a film released in August called Phantom. It was based on a covert Indian operation to kill the 2008 Mumbai attack plotters, including Hafiz Saeed, the former head of militant group Lashkar-e-Taiba, which is accused of carrying out the attack.
"The Americans killed Osama by barging in, why can't we do the same?" says the agent in charge of the mission, played by Muslim actor Saif Ali Khan.
India 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 nuclear weapons could quickly escalate.
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