The total number of warheads stockpiled for potential use among the five recognized nuclear powers of the United States, Russia, China, France and Britain plus the de facto nuclear states of India, Pakistan, North Korea and Israel increased by nine to 9,585, the Stockholm International Peace Research Institute said.
Including retired warheads, the overall nuclear inventories of the nine countries are projected to have dropped by 391 to 12,121, the think tank said in its annual report.
"The number and types of nuclear weapons in development have increased as states deepen their reliance on nuclear deterrence," it added.
Regarding China, the think tank said it could have at least as many intercontinental ballistic missiles, which can be used to deliver nuclear warheads, as either Russia or the United States by the turn of the decade, although its stockpile of warheads is still expected to remain much smaller than the two nuclear powers.
North Korea was estimated to have now assembled around 50 warheads, up 20 from 2023, and possesses enough fissile material to reach a total of up to 90 warheads, it said.
"Like several other nuclear-armed states, North Korea is putting new emphasis on developing its arsenal of tactical nuclear weapons," said Matt Korda, associate researcher with SIPRI's Weapons of Mass Destruction Programme.
"Accordingly, there is a growing concern that North Korea might intend to use these weapons very early in a conflict," Korda added.
Russia and the United States had 5,580 and 5,044 warheads respectively, accounting for nearly 90% of the world's total, the report said.
An estimated 3,904 warheads were deployed on missiles and aircraft, up by 60 from the previous year, including 1,710 by Russia and 1,770 by the United States.
The think tank says China is thought to have deployed 24 warheads on missiles.
"While the global total of nuclear warheads continues to fall as Cold War-era weapons are gradually dismantled, regrettably we continue to see year-on-year increases in the number of operational nuclear warheads," SIPRI Director Dan Smith said.
"The trend seems likely to continue and probably accelerate in the coming years and is extremely concerning," Smith added.