Israel is widely believed to possess nuclear weapons, though the country neither acknowledges nor denies the existence of a nuclear arsenal. Israel is not a party to the Nuclear Non-Proliferation Treaty (NPT) and has not accepted IAEA safeguards on some of its principle nuclear activities. Their policy of nuclear opacity has been generally tolerated by both allies and adversaries.
A Special National Intelligence Estimate — SNIE 100-8-60 from 8 December 1960 — that formally determined that "Israel is engaged in construction of a nuclear reactor complex in the Negev near Beersheba" and "plutonium production for weapons is at least one major purpose of this effort." The SNIE estimated "that Israel will produce some weapons grade plutonium in 1963-64 and possibly as early as 1962." A significant portion of the SNIE is still classified.
https://armscontrolcenter.org/countries/israel/
https://www.wilsoncenter.org/publication/the-us-discovery-israels-secret-nuclear-project