India's defence minister Rajnath Singh (left) and Pakistan's Prime Minister Imran Khan (right).Credit: Hindustan Times/Getty, Aamir Qureshi/Getty

Nuclear tensions are escalating between south Asia’s two superpowers — India and Pakistan — following the Indian defence minister's announcement earlier this month that India may revoke its current commitment to only use nuclear weapons in retaliation for a nuclear attack, known as ‘no first use’.

Some experts watching the situation have told Nature that the risk of a conflict between the two countries has never been greater since they both tested nuclear weapons in 1998.

“It’s very explosive right now and I am really concerned it could get worse,” says Atta-ur-Rahman, professor of chemistry at the University of Karachi in Pakistan and a science adviser to Pakistan's prime minister Imran Khan. Khan has talked up the risks of nuclear war between the two countries on several occasions since being elected a year ago.

Vipin Narang, who studies nuclear proliferation at the Massachusetts Institute of Technology in Cambridge, says the statement from defence minister Rajnath Singh creates ambiguity in India’s no-first-use policy, and “essentially renders it meaningless”.

Satinder Kumar Sikka, a condensed matter physicist who was part of India’s 1998 nuclear-weapons testing team, argues that India should be able to use nuclear weapons if there is an increased risk that Pakistan would do so first. “If we are threatened by Pakistan, we have every right to retaliate,” he says.

Others caution against reading too much into the present war of words, emphasizing that a conventional war or a nuclear armed conflict will not be triggered just because of strong language from both sides.

Nature examines the background for the latest escalation, what it means and what could happen next.

What is no first use and who else has adopted it?

Of the world’s eight declared nuclear-weapons states, only China and India have an unambiguous no first use nuclear weapons policy. This is a commitment only to use nuclear weapons in response to a nuclear attack and never in retaliation for one using conventional weapons. Such a policy also includes comprehensive protocols in which activating nuclear weapons would only ever be a last resort.

India tested its first nuclear weapon in 1974 and the government committed to no first use in 2003, five years after conducting a second set of nuclear-weapons tests on 11 and 13 May 1998. The intention in declaring no first use was partly to help defuse tensions with its neighbour, which had responded to India’s second test with its own nuclear tests the same month.

Over the past two decades, Pakistan has amassed 150–160 nuclear missiles, to India’s 130–140, according to the Stockholm International Peace Research Institute. Both countries, moreover, have advanced nuclear weapons, as well as ballistics research and development programmes.

Why doesn’t Pakistan have a no first use policy?

According to Feroz Hassan Khan, who teaches security studies at the Naval Postgraduate School in Monterey, California, if Pakistan were to adopt the same policy, that would negate its reason for developing nuclear weapons in the first place.

Khan, who was a member of Pakistan’s nuclear weapons planning staff in the early 2000s, says that the country began developing nuclear weapons in the 1970s because it had fewer armed forces than India and knew it would lose a conventional war unless it developed more powerful military technology. At the time, Pakistan’s then prime minister said his people would “eat grass, leaves or go hungry” if that is what it took to get nuclear weapons.

India and Pakistan have been at loggerheads before: why is the current situation such a big deal?

When India’s defence minister Singh said on 16 August that the country’s long-held no first use nuclear weapons doctrine could change, “depending on circumstances”, this was not the first time a senior politician had floated the idea.

But the minister’s statement came at a time when the two countries’ governments are barely on speaking terms. A week earlier, India announced that Kashmir — a disputed northern region claimed by both India and Pakistan and currently divided into two areas administered by each country, respectively — would no longer need a separate constitution from the rest of India. Indian-administered Kashmir would, moreover, be partitioned into two territories. A curfew and communications blackout followed in Indian-administered Kashmir, which is very slowly being lifted.

Pakistan’s government has been trying to persuade the international community through the United Nations to censure India’s government. India’s opposition parties also oppose what is happening in Kashmir. But India’s government, led by Prime Minister Narendra Modi, says that its changes will help Kashmiri society and its economy to develop, and that neither country needs outside help to resolve their differences.

Relations have been on a knife-edge since February, when a Pakistan-based militant group, Jaish-e-Mohammad, claimed responsibility for the deaths of 40 paramilitary police officers in Indian-administered Kashmir. India responded with air strikes that hit targets inside Pakistan. For a few days in February it did seem as if war would break out. Pakistan and India have previously fought wars with each over the region.

What might happen next?

Analysts say that a nuclear conflict — although closer — is still remote. But they also agree that rhetoric from both sides combined with the possibility of even a small change to India’s no first use principle is not safe.

For example, if India firms up the change in its no first use policy, Pakistan might take this as a signal that India could pre-emptively strike at Pakistani nuclear installations, says Narang. And that might, in turn, prompt Pakistan to use up all its nuclear weapons first. “And so, you get this destabilising dynamic where as soon as the crisis becomes nuclearized, there is an incentive for both sides to go first,” Narang says..

How likely are these scenarios?

Ramamurti Rajaraman, emeritus professor of physics at the Jawaharlal Nehru University in Delhi, calls the escalating rhetoric a “war of words” — that will not on its own lead to military action.

However, the increasing tensions combined with references to nuclear conflict from both sides mean that the two countries are now likely to have changed the status of their nuclear weapons readiness from “peacetime” to “crisis”, says Khan.

In practice, this means moving the three main physical components of a weapon — the warhead, missile-delivery system and fissile material core — either assembled or closer to where they need to be, ready for launch. In peacetime, each component is kept at a different location, for safety and security.

According to Khan, such a state of readiness for a strike heightens the risk of a nuclear accident, but is not in itself a sign that war will happen.

But if there is another attack inside India — as happened in February — India’s armed forces might again respond with force. That would precipitate a reaction from Pakistan’s military, prompting a retaliation from India. Unless one side voluntarily holds back, the prospect of such military escalation concerns analysts because it could eventually lead to strikes against nuclear targets.