India has "one of the largest nuclear power programmes" among developing nations, the Institute for Science and International Security said in Washington.
"An estimate of India's nuclear arsenal can be derived by considering its weapon-grade plutonium stock. The resulting estimate has a median of 138 nuclear weapons equivalent with a range of 110 to 175 weapons equivalent," a report released on Monday by the think-tank.
"However, the actual number of nuclear weapons India built from its stocks of weapon-grade plutonium must be less. When accounting for the amount of plutonium in the weapons production pipelines and in reserves, it is reasonable to assume that only about 70 per cent of the estimated stock of weapon-grade uranium is in nuclear weapons," the report said.
"Thus the predicted number of weapons made from its weapon-grade plutonium at the end of 2014 is about 97 with a range of 77-123. These values are rounded to 100 nuclear weapons with a range of 75-125 nuclear weapons," the report co-authored by David Albright and Serena Kelleher-Vergantini said.
Notably, Albright had led anti-India campaign both at the Congress and among the think-tanks against the Indo-US civil nuclear deal.
The report 'India's Stocks of Civil and Military Plutonium and Highly Enriched Uranium, End 2014' concludes that India has "one of the largest nuclear power programmes among developing nations".
The report estimated that India has made 100-200 kilogrammes of weapon-grade uranium for nuclear weapons.
"Faced with a lack of information but evidence that India has produced HEU (highly enriched uranium) for nuclear weapons, it is assumed that India has made 100-200 kilogrammes of weapon-grade uranium for nuclear weapons. Of course, this estimate is highly uncertain," the report said.
"It has a substantial stock of nuclear weapons made from weapon-grade plutonium, and perhaps some thermonuclear weapons that rely on both weapon-grade plutonium and weapon-grade uranium," the report said.
Noting that an estimate of India's nuclear arsenal can be derived by considering its plutonium and highly enriched uranium stocks, the report said India separates plutonium produced primarily in a set of small, dedicated reactors and a smaller amount produced in nuclear power reactors.
"However, India also has a growing gas centrifuge programme capable of producing significant amounts of HEU mostly for naval reactor fuel and perhaps for nuclear weapons, including thermonuclear weapons," it said, alleging that India is not transparent about its fissile material stocks.
The report estimates India's stocks of separated plutonium and highly enriched uranium as of the end of 2014.