A report by the Institute For Science and International Security (ISIS) released last week claims Israel has 115 nuclear warheads and some 660 kg of plutonium.
Israel has never confirmed or denied having nuclear weapons under a policy of ambiguity aimed at deterring longtime Arab and Muslim adversaries.
The report, written by institute founder David Albright, is based largely on information leaked by Mordechai Vanunu in 1986, as well as intelligence reports, media reports and other research.
In his report, Albright reviews Israel's alleged nuclear activities at the Dimona nuclear reactor which started, he claims, shortly before the 1967 Six-Day War.
The report's assessment that Israel has some 660 kilograms of plutonium is slightly lower than the amount estimated by the International Panel on Fissile Materials (IPFM) because Albright believes the Dimona reactor's production capabilities are lower than what the IPFM researchers believe.
"The actual number of Israeli nuclear weapons is a closely guarded secret," Albright explains.
"Israel has a wide range of delivery vehicles for its nuclear weapons. With French assistance in the 1960s, Israel developed the nuclear-capable Jericho ballistic missile. It has developed several improved missiles since then on its own, as well as nuclear-capable cruise missiles. It also has aircraft that can deliver nuclear weapons. It may have the capability to launch nuclear-tipped cruise missiles from its submarines."
According to the report, Israel also illegally procured a wide variety of high tech nuclear equipment from abroad, that can be used both for civilian and military purposes.
"In the 1990s, under US pressure, senior Israeli government officials stated that Israel committed not to violate supplier controls to acquire dual-use goods for its nuclear programs," Albright notes.
However, "occasional procurements possibly intended for the nuclear program are observed despite this pledge," he notes.
Albright's estimate of the number of nuclear warheads Israel allegedly has is based on the assumption each warhead has 3-5 kilograms of plutonium. Based on the amount of plutonium he believes Israel has, it amounts to 165 warheads.
But Albright estimates Israel did not use all of the plutonium in its possession to build warheads, so the number of nuclear warheads it actually has is more likely around 115, as of the end of 2014.