Israel is improving its main nuclear site in the southern Negev, according to the Stockholm International Peace Research Institute's annual armaments assessment, released on Monday.

"Israel—which does not publicly acknowledge possessing nuclear weapons—is also believed to be modernizing its nuclear arsenal and appears to be upgrading its plutonium production reactor site at Dimona," the group said in its SIPRI Yearbook 2024.

The upgrade was part of a general trend, with all nine nuclear-armed states continuing to modernize their arsenals and several deploying "new nuclear-armed or nuclear-capable weapon systems in 2023," the report stated.

"[T]he number and types of nuclear weapons in development have increased as states deepen their reliance on nuclear deterrence," it added.

SIPRI estimates that Israel has 90 nuclear warheads, placing it second-to-last in terms of quantity among the nine nuclear-armed states: the United States, Russia, the United Kingdom, France, China, India, Pakistan and the Democratic People’s Republic of Korea (North Korea).

However, according to SIPRI North Korea possesses fewer warheads (an estimated 50). "Countries are ordered by date of first known nuclear test; however, there is no conclusive open-source evidence that Israel has tested its nuclear weapons," SIPRI explained.

There are 12,121 warheads in the total global inventory as of January 2024, of which 9,585 were in military stockpiles for potential use. Of those, an estimated 3,904 are deployed with missiles and aircraft and the rest are in storage.

Around 2,100 warheads are in a "state of high operational alert" on ballistic missiles. Virtually all those warheads belong to Russia or the United States, "but for the first time China is believed to have some warheads on high operational alert," according to the report.