The FAS draws its conclusions from comparisons of the latest images with pictures of the Dimona facility taken by a US reconnaissance satellite in 1971.
The photographs of the secret Israeli nuclear facility at Dimona in the Negev desert appear on the website of the Federation of American Scientists (FAS).
The new images were obtained last month by Space Imaging Corporation's Ikonos satellite.
The FAS draws its conclusions from comparisons of the latest images with pictures of the Dimona facility taken by a US reconnaissance satellite in 1971.
Part of the FAS work is to monitor non-conventional weapons capabilities throughout the world.
The pictures "indicate that no new cooling towers were constructed in the years between 1971 and 2000," the FAS report says.
"This strongly suggests that the reactor's power level has not been increased significantly during this period. This would suggest an annual production rate of plutonium of about 20kg."
Nuclear arsenal
"Based on plausible upper and lower bounds of the operating practices at the reactor, Israel could have thus produced enough plutonium for at least 100 nuclear weapons, but probably not significantly more than 200 weapons," the FAS said.
The latest pictures have been shown on Israeli television and published in the Israeli daily Yediot Aharonoth.
Israeli censorship laws allow local media to quote foreign reports, provided the source is mentioned.
Israel is now the only state with nuclear weapons that does not admit to having such weapons. It has always refused to allow international inspection of the Dimona facility, and is among the few states that have refused to sign the nuclear non-proliferation treaty.
Israel maintains what is known as a policy of 'nuclear ambiguity', saying that it will not be the first country to introduce them to the Middle East.
In 1986 Mordechai Vanunu, a former technician at the site, was jailed for 18 years for providing information about Dimona, including photos published in the UK's Sunday Times.
Israeli-US 'understanding'
The Israeli authorities have said they want to question Avner Cohen, an Israeli writer living in self-imposed exile in the United States, in connection with his 1998 book "Israel and the Bomb".
The book argues that there was an Israeli-US understanding that Washington would turn a blind eye to Israel's nuclear programme provided Israel kept a low profile and did not carry out nuclear tests.
The Dimona reactor has been operating since 1965.
The FAS says that by the late 1990s the US intelligence community estimated that Israel possessed 75-130 nuclear weapons.
They would include warheads for mobile Jericho-1 and Jericho-2 missiles, bombs for Israeli aircraft and possibly other tactical nuclear weapons.