Israel's nuclear weapons arsenal includes 115 warheads, according to a new report by the Institute for Science and International Security, a Washington, DC-based think tank.

The arsenal represents what Israel has been estimated to amass since it developed its first nuclear weapon shortly before the Six-Day War in 1967.

The study, which was conducted as part of more comprehensive evaluation of the worldwide inventory of plutonium, estimates that Israel has produced about 660 kilograms of plutonium at the Dimona reactor since operations began in 1963, which would allow it to have 115 nuclear weapons today.

The report acknowledges that the actual number is not publicly known. Israel is one of nine nations that has a nuclear arsenal, but is the only one that does not comment on its existence. Other studies have estimated that Israel has between 80 and 200 nuclear weapons.

A single nuclear bomb requires three to five kilograms of plutonium, the study estimated.

"Based on the total production of plutonium, the median for the number of nuclear weapons is about 165 with a standard deviation of 33 and a full range of about 90-290 weapons. Likely, Israel did not build this many nuclear weapons. A reasonable assumption is that the number of deployed weapons is 30% lower, or 115 nuclear weapons as of the end of 2014," says the report, written by former UN nuclear inspector David Albright.

The report also says Israel has nuclear-capable cruise missiles and that, despite 1990s pledges to the United States not to acquire "dual-use materials" from abroad, it sometimes buys advanced equipment for its nuclear weapons program from abroad.

Israel, which has no safeguards agreement with the International Atomic Energy Agency, has been an obstacle to the establishment of a "nuclear-free zone" in the Middle East.