NEW DELHI - One of the great ironies of the twentieth century is that so significant a scientific advance as the ability to split the atom did not bring greater security. While North Korea has grabbed world headlines again with its failed launch of a long-range missile, and its threats to stage an underground nuclear test, Indians are protesting against the construction of nuclear power plants, owing to growing concerns about safety.

The nuclear bomb was the first technological advance to follow from splitting the atom, and countries that could adopt it quickly did so, without fully understanding its destructive power. Today, the complex engineering capacity needed to produce nuclear weapons - skills restricted to a few countries through the 1970's - is rather commonplace. The number of countries that can build such devices has multiplied, as has the destructive power of these weapons.

This democratisation of nuclear capacity has fueled anxiety about weapons proliferation among states - even a basket-case economy like North Korea has joined the club - and of 'privatisation' of weapons by terrorist groups. As a result, in October 2010, the United States and Russia - the world's two largest nuclear powers - joined 80 other countries in the Global Initiative to Combat Nuclear Terrorism.

In turn, retired US and Russian military and intelligence established the Elbe Group, named for the river where the two countries' forces met in the closing days of World War II. By May 2011, the group produced a 'Joint Threat Assessment on Nuclear Terrorism,' which outlines the threat in graphic detail.

The report reflects a growing consensus that 'terrorists could obtain nuclear materials and use them,' concluding gravely: 'If current approaches toward eliminating the threat are not replaced with a sense of urgency and resolve, the question will become not if, but when, and on what scale, the first act of nuclear terrorism occurs.'

After Osama bin Laden was killed in May 2011, an illusion took hold that, with al-Qaeda diminished, the threat of nuclear terrorism had receded as well. But terrorist groups abound in Pakistan, and the country is increasing its stockpile of fissile material faster than anyone else in the world. Indeed, Pakistan has begun producing tactical nuclear weapons, which must be kept dispersed, and are thus less secure.

Seizures of illegal fissile material have declined since the 1990's, when nuclear states disposed of roughly 480 kilograms of highly enriched uranium - a building block for a nuclear bomb. Kazakhstan led the way. Graham Allison of Harvard, an authority on nuclear terrorism, recounts that as assistant secretary of defense in the Clinton administration in early 1993, he received a phone call from William Courtney, the ambassador in Kazakhstan, who said that a stash of highly enriched uranium had been found in a warehouse in Almaty, secured with only a padlock. Reportedly, enough uranium to produce 35 or 40 bombs was retrieved.

Do other forgotten stores lie around the globe?

One site that has not been forgotten is North Korea. Having agreed in February to halt nuclear tests, uranium enrichment, and long-range-missile launches in exchange for food aid, the country nonetheless attempted to launch its most powerful rocket yet. Moreover, the launch's failure may have made a third nuclear weapons test more likely.

There are two main obstacles to eradicating threats like those posed by North Korea: the sense that a nuclear weapon is the trump card in defence of national sovereignty, and insufficient progress on nuclear disarmament by the world's main nuclear states (the US, Russia, China, France, and the United Kingdom). Indeed, the US and Russia have merely repeated their commitment, made in 2010, to dispose of 68 tons of weapons-grade plutonium. When they will do so is unknown. But if they do not act, no one else will.

Such inertia is unacceptable. Perhaps the newly restarted nuclear talks with Iran can break the ice and advance the process of global nuclear disarmament, but that seems a slim hope, at best. Even Brazil, once a staunch advocate for nuclear non-proliferation, now insists that all states have an inalienable right to enrich uranium for peaceful purposes.

It is difficult to imagine where a catalyst for change will arise. A nuclear summit in Seoul last month generated little momentum to diminish the threat posed by rogue and unstable nuclear power. Roughly 40 countries are operating or constructing nuclear reactors to meet their energy needs. What if all wish to become nuclear weapons states?

In fact, their intentions might not matter. The more nuclear capacity there is around the world, the greater the danger that terrorists' will gain access to it. And now, I fear, we have reached the point at which the question is no longer whether that will happen, but when.

Jaswant Singh, a former Indian finance minister, foreign minister, and defense minister, is the author of Jinnah: India - Partition - Independence.