Pakistan started focusing on nuclear development in January 1972 under the leadership of Prime Minister Zulfiqar Ali Bhutto. Pakistan's nuclear weapons development program was in response to India's development of nuclear weapons. Bhutto called a meeting of senior scientists and engineers on January 20, 1972, at Multan. It was here that Bhutto rallied Pakistan's scientists to build the atomic bomb for national survival. At the Multan meeting, Bhutto also appointed a Pakistani nuclear engineer, Munir Ahmad Khan, as chairman of Pakistan Atomic Energy Commission, who till then had been working as Director of Nuclear Power and Reactor Division at IAEA, in Vienna. This marked the beginning of Pakistan's pursuit of nuclear capability. Following India's surprise nuclear test, code named Smiling Buddha in 1974, the goal to develop nuclear weapons received considerable impetus.
Consequently, Dr. Abdul Qadeer Khan, a metallurgical engineer, working in a Dutch research firm used URENCO blueprints for designing the ultra centrifuges at Kahuta (near Islamabad) also joined Pakistan's nuclear weapons-grade Uranium enrichment program. The uranium enrichment program had been launched in 1974 by PAEC chairman Munir Ahmad Khan as Project-706. AQ Khan joined the project in the spring of 1976 and was made Project-Director in July 1976 after taking over from Sultan Bashiruddin Mahmood. Although in 1983, A.Q.Khan was convicted of the theft of these blueprints, the conviction was overturned on some technicality.
A few weeks after India's Shakti (Power) operation (second nuclear test), on 28 May 1998, Pakistan detonated 5 nuclear devices in the Chagai Hills in the Chaghai district, Baluchistan. This operation was named Chagai-I by Pakistan. Pakistan's fissile material production takes place at Kahuta and Khushab/Jauharabad, where weapons-grade Plutonium is made; the latter, allegedly, with the assistance of Chinese-supplied technology.
The Natural Resources Defense Council (NRDC) estimates that Pakistan has built 24-48 HEU-based nuclear warheads with HEU reserves for 30-52 additional warheads. The US Navy Center for Contemporary Conflict estimates that Pakistan possesses between a low of 35 and a high of 95 nuclear warheads, with a median of 60.
The NRDC's and the Carnegie Foundation's estimates of approximately 50 weapons are from 2002-3 estimations. In 2000, US Military intelligence estimated that Pakistan's nuclear arsenal may be as large as 100 warheads.The actual size is hard for experts to gauge owing to the secrecy which surrounds the program in Pakistan.
The United States government responded to Pakistan's testing of nuclear weapons in 1998 with sanctions. Following the Gulf War, the United Nations put in place decade-long sanctions against the Government of Iraq with the stated purpose of preventing the government from developing weapons of mass destruction. The 2003 Invasion of Iraq was partly based on the idea that Iraq had developed, or was in the process of developing, weapons of mass destruction but the intelligence reports were later proven to be flawed.