Finally, on 28 May 1998, a few weeks after India's second nuclear test (Operation Shakti), Pakistan detonated five nuclear devices in the Ras Koh Hills in the Chagai district, Balochistan. This operation was named Chagai-I by Pakistan, the underground iron-steel tunnel having been long-constructed by provincial martial law administrator General Rahimuddin Khan during the 1980s. The last test of Pakistan was conducted at the sandy Kharan Desert under the codename Chagai-II, also in Balochistan, on 30 May 1998. Pakistan's fissile material production takes place at Nilore, Kahuta, and Khushab Nuclear Complex, where weapons-grade plutonium is refined. Pakistan thus became the seventh country in the world to successfully develop and test nuclear weapons. Although, according to a letter sent by A.Q. Khan to General Zia, the capability to detonate a nuclear bomb using highly enriched uranium as fissile material produced at KRL had been achieved by KRL in 1984.