Global stockpiles of nuclear weapons are increasing and reversing decades of nuclear disarmament, a top conflict think tank reported Monday.

For years, an annual decrease in the global inventory of nuclear weapons combined with the disarmament of retired warheads by the U.S. and Russia has outstripped the number of new warheads. But a report released Monday by the Stockholm International Peace Research Institute (SIPRI) found this trend will be reversed in the coming years as dismantlement slows while the deployment of new nuclear weapons increases.

“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,” said Hans M. Kristensen, associate senior fellow with SIPRI’s Weapons of Mass Destruction program.

“Instead, we see a clear trend of growing nuclear arsenals, sharpened nuclear rhetoric and the abandonment of arms control agreements,” he added.

Out of the nine nuclear-armed states — the U.S., U.K., Russia, France, China, Pakistan, India, Israel and North Korea — all are upgrading existing weapons and adding new versions to their stockpiles.

According to SIPRI’s 2025 yearbook, an estimated 12,241 nuclear warheads existed worldwide as of January. Of those, approximately 9,614 are held in military stockpiles ready for potential use, with more than 2,100 kept on high alert — primarily by the United States and Russia.

China is leading the pack, with its nuclear arsenal having grown by 20 percent in just one year to an estimated 600 warheads. Projections indicate it could rival U.S. and Russian stockpiles by 2030. Meanwhile, India, Pakistan and Israel are also actively expanding or modernizing their nuclear capabilities.

The study’s findings come amid escalating attacks between Iran and Israel and just a few weeks after stalled peace negotiations between Russia and Ukraine. Israel’s recent targets in Iran included military sites and prominent nuclear scientists.

On the early 2025 tensions between India and Pakistan, Matt Korda, associate senior researcher at SIPRI, said that strikes on nuclear-related military infrastructure risked turning a conventional conflict into a nuclear crisis. “This should act as a stark warning for states seeking to increase their reliance on nuclear weapons.”

Reflecting concerns over the confrontation between Israel and Iran in the Middle East, the International Atomic Energy Agency said Monday it was monitoring the situation “very carefully” and confirmed that radiation levels remain stable following recent bombings of the Iranian uranium enrichment plant in Natanz.

“The IAEA is ready to respond to any nuclear or radiological emergency within an hour,” said IAEA Director Rafael Mariano Grossi. “For the second time in three years, we are witnessing a dramatic conflict between two member states, in which nuclear facilities are under fire and their safety compromised.”