Nearly all of the world's nine nuclear-armed states were modernising and upgrading existing weapons and adding new ones, the Stockholm International Peace Research Institute (SIPRI) said in its annual report on the world's arsenals.
"The era of reductions in the number of nuclear weapons in the world, which had lasted since the end of the Cold War, is coming to an end," SIPRI analyst Hans M Kristensen said.
"Instead, we see a clear trend of growing nuclear arsenals, sharpened nuclear rhetoric and the abandonment of arms control agreements."
The dismantling of retired warheads by the United States and Russia since the end of the Cold War had led to a considerable decline, but this effect was now slowing, while the deployment of new nuclear weapons was accelerating, SIPRI said.
It noted that the US and Russia possessed around 90 per cent of all nuclear weapons and that both were implementing extensive modernisation programs that could increase the size and diversity of their nuclear arsenals in the future.
The nine states - the US, Russia, France, the United Kingdom, China, India, Pakistan, North Korea and Israel - have a total inventory of 12,241 warheads, down from 12,405 last year, according to the SIPRI figures, which are estimates.
The deployed warhead total is much lower at 3912.
The US has 1770, Russia 1718, France 280, the UK 120 and China 24.
