Strategic affairs researchers in India who analysed uranium supplies and demand in Pakistan have estimated that Islamabad has between 112 and 156 nuclear weapons, an assessment 'significantly lower' than earlier estimates by some international nuclear specialists.

The researchers at the National Institute of Advanced Studies (NIAS), Bangalore, say their analysis suggests that Pakistan has since 2010 faced severe uranium constraints and 'could not have pursued' uranium or plutonium-based weapons 'as vigorously as generally believed'.

The International Panel for Fissile Materials (IPFM), an independent group of arms control and non-proliferation experts, had estimated in 2015 that Pakistan had an inventory of about 3,100kg weapon-grade highly enriched uranium (HEU) and 190kg of weapon-grade plutonium.

These amounts of material, some experts have argued, would be theoretically enough to produce 204 to 306 warheads, assuming each warhead's core uses 12 to 18kg of HEU or 4 to 6kg of plutonium.

For their analysis, NIAS researchers Lalitha Sundaresan and Kaveri Ashok examined Pakistan's domestic demand for uranium to run the Karachi civilian nuclear power reactor for operations up to 2014 and nuclear fuel demand imposed by four plutonium reactors set up by Pakistan in 1996, 2010, 2013 and 2015.

They also studied available uranium supplies given constraints imposed by the closure of Pakistan's Bagalchur uranium mine in 2000 and the shutdown of milling operations at a site near Dera Ghazi Khan in 2005.

These changes in supply-demand occurred alongside what the researchers say is a shift in Pakistan's nuclear strategy -- after the 1999 Kargil war -- to bolster its arsenal with tactical (low-yield) nuclear weapons based on plutonium. This shift towards plutonium would have eaten away uranium intended for enrichment.

Under these supply-demand circumstances, Sundaresan and Ashok estimate that Pakistan has only between 78 and 104 HEU weapons and between 34 and 52 plutonium weapons. Their analysis was published on Monday in Current Science, a journal of the Indian Academy of Sciences.

'This essentially means that Pakistan has fewer numbers while the world at large believes it has more,' Sundaresan told The Telegraph.

'If Pakistan is indeed producing the amounts of fissile materials as reported earlier, despite its uranium constraints, the question of Pakistan's uranium sourcing especially after 2010 needs to be addressed. Without a deeper understanding of this sourcing, it is difficult to believe Pakistan has the arsenal it is reported to possess.'.