Pakistan's ISI and Special Service Group (SSG) became actively involved in the conflict against the Soviets. The SSG created a unit called the Black Storks who were SSG men dressed as Afghan Mujahideen during the Soviet–Afghan War. They were then flown into Afghanistan and provided the Mujahideen with support. After Ronald Reagan was elected in 1980, US aid for the Mujahideen through Pakistan significantly increased. In retaliation, the KHAD, under Afghan President Mohammad Najibullah, carried out (according to the Mitrokhin archives and other sources) a large number of terrorist operations against Pakistan, which also suffered from an influx of weaponry and drugs from Afghanistan. Pakistan took in 3 million Afghan refugees (mostly Pashtun) who were forced to leave their country. Although the refugees were controlled within Pakistan's largest province, Balochistan, then under martial law ruler General Rahimuddin Khan, the influx of so many refugees – believed to be the largest refugee population in the world – into several other regions had a lasting impact on Pakistan.