Israel, whose prime minister withdrew Friday from next week's US-hosted nuclear summit, is viewed as the sixth country to have acquired nuclear weapons -- a title it has neither denied nor confirmed.
Analysts at British defense specialists Jane's believe the Jewish state has between 100 and 300 nuclear warheads, putting them among the more advanced nuclear weapons states and roughly on a par with Britain.
The London-based International Institute of Strategic Studies (IISS) estimates Israel has "up to 200" warheads delivered on land-based short-range Jericho 1 and medium-range Jericho 2 missiles.
The Nuclear Threat Initiative, a US advocacy group co-created by Ted Turner, the founder of CNN, puts the figure at 100 to 200.
Israel is the only nuclear power in the Middle East with a program dating back to the 1950s under Israel's first prime minister, David Ben Gurion.
It was developed with the help of France and is centered on the Dimona reactor in the southern Negev desert.
According to Jane's, the Israeli strategic force could be deployed by the Jericho 2 missile, which has a range of up to 4,500 kilometers (2,800 miles), or the five-year-old Jericho 3, which reaches up to 7,800 kilometers.
It is also believed to be able to deploy by air, using F-16 fighter jets, and even by sea through its submarine fleet, providing an opportunity for a second strike if its land systems are attacked.
Israel acquired three diesel-powered Dolphin-class submarines in 1999-2000 which are capable of launching adapted Harpoon cruise missiles fitted with nuclear warheads.
In addition, Jane's says some observers believe Jerusalem has developed tactical nuclear weapons such as landmines and artillery shells.
"Some analysts believe that Israel probably keeps most, if not all, of its nuclear arsenal in an unassembled mode," the latest Jane's briefing says, adding that "fully functional weapons could be completed in a matter of days".
Israeli Prime Minister Benjamin Netanyahu abruptly withdrew Friday from next week's nuclear summit in Washington, underscoring Israeli reluctance to expose its own nuclear program to scrutiny.