A Swedish arms watchdog says the world’s stockpiles of nuclear weapons are expected to increase in coming years, reversing a decline seen since the end of the Cold War.

The Stockholm International Peace Research Institute, or SIPRI, said Monday that all nine nuclear-armed countries are increasing or upgrading their arsenals.

“There are clear indications that the reductions that have characterized global nuclear arsenals since the end of the Cold War have ended,” said Hans M. Kristensen, a researcher with SIPRI’s Weapons of Mass Destruction Program and director of the Nuclear Information Project at the Federation of American Scientists.

The U.S. and Russia, which hold 90% of the world’s atomic weapons, saw their inventories decline in 2021 due to the dismantling of warheads retired from military service years ago. Their useable military stockpiles remained relatively stable and within the limits set by a nuclear arms reduction treaty, SIPRI said.

The research institute said that the other nuclear states — Britain, France, China, India, Pakistan, Israel and North Korea — are either developing or deploying new weapon systems, or have announced their intention to do so. Israel has never publicly acknowledged having such weapons.

“All of the nuclear-armed states are increasing or upgrading their arsenals and most are sharpening nuclear rhetoric and the role nuclear weapons play in their military strategies,” said Wilfred Wan, the director of SIPRI's Weapons of Mass Destruction Program. “This is a very worrying trend."