The nine nuclear-armed states jointly spent nearly $119 billion on their arsenals last year, up 19 percent from 2024, according to the International Campaign to Abolish Nuclear Weapons (ICAN).

"A new nuclear arms race is upon us," its report warned.

ICAN, and a separate study by the Stockholm International Peace Research Institute (SIPRI) released on Monday, voiced alarm at the growing nuclear risk amid swelling geopolitical tensions.

The dramatic spending hike on nuclear weapons came as countries rushed to modernise their arsenals and deploy more of their stockpiles, the studies showed.

Susi Snyder, ICAN's director of programmes and co-author of the latest report, said the scale-up, coupled with fears that artificial intelligence could increase the risk of nuclear weapons use, was deeply alarming.

"To be perfectly honest, I'm terrified," she told AFP.

- 'Risks are rising' -

SIPRI's report highlighted that the total estimated number of nuclear warheads had been declining for decades, falling to 12,187 at the start of this year, but warned the number of weapons available for potential use had risen, to 9,745.

"Even though we have lower numbers of nuclear weapons, the level of nuclear dangers and nuclear risks are rising," SIPRI director Karim Haggag told AFP.

He pointed to worrying signs, including the breakdown in strategic arms controls and competition between great powers with nuclear arms.

SIPRI predicted that overall nuclear arms stockpiles were likely to begin growing again in coming years "as the pace of dismantlement is slowing, while the deployment of new nuclear weapons is accelerating".

The United States and Russia together hold around 83 percent of the world's nuclear arms stockpile, with more than 5,000 warheads each. China is expanding its nuclear arsenal faster than any other country, SIPRI said, estimating that it counts around 620 warheads.

"Intensifying geopolitical competition means a very strong incentive on the part of China to increase its reliance on nuclear weapons," Haggag said.

ICAN's report indicated that all nuclear-armed states, which also include Britain, France, India, Israel, North Korea and Pakistan, were increasing investments in their arsenals.

The nine countries jointly spent nearly $17 billion more last year than in 2024 on the weapons of mass destruction.

Washington spent more than all the other countries combined, dishing out $69.2 billion on nuclear weapons in 2025 -- an increase of $12.4 billion from a year earlier, ICAN said.

The United States was followed by China, which was estimated to have spent $13.5 billion last year, then Britain at $12.6 billion and Russia at $9.5 billion, it said.

Over the past five years, it determined that the nine countries had spent over $470 billion on their arsenals.

- Long lifespans -

Those investments are expected to grow going forward.

Examining longer term projections, ICAN highlighted figures from Britain, France and the United States showing plans to spend billions to develop and maintain nuclear weapons systems well into the next century.

Other countries too were introducing new weapons systems with long lifespans, it said.

The report pointed out that planned new US Sentinel intercontinental ballistic missiles were expected to remain operational past 2100, while swelling US plutonium pit production indicated that the country's warheads would last through 2120.

That will mean significant investment, with US nuclear arms spending over just the decade between 2025 and 2034 projected at close to $1 trillion.

Researchers said the huge sums were particularly jarring at a time when the global humanitarian system was reeling from dramatic funding cuts.

Just a single day of nuclear weapons spending last year could have provided food security to more than two million people, they said.

Instead of providing aid or healthcare for their populations, the nuclear-armed states were investing in "an arsenal that they themselves know they cannot use without committing a war crime", Snyder said.

"There seems to be a total disconnect from reality."