Due to ideological differences, Pakistan opposed the Soviet Union in the 1950s. During the Soviet–Afghan War in the 1980s, Pakistan was one of the closest allies of the United States. Relations between Pakistan and Russia have greatly improved since 1999, and co-operation in various sectors has increased. Pakistan has had an "on-and-off" relationship with the United States. A close ally of the United States during the Cold War, Pakistan's relationship with the US soured in the 1990s when the latter imposed sanctions because of Pakistan's secretive nuclear development. Since 9/11, Pakistan has been a close ally of the US on the issue of counterterrorism in the regions of the Middle East and South Asia, with the US supporting Pakistan with aid money and weapons. Initially, the US-led war on terrorism led to an improvement in the relationship, but it was strained by a divergence of interests and resulting mistrust during the war in Afghanistan and by issues related to terrorism. The Pakistani intelligence agency, the ISI, was accused of supporting Taliban insurgents in Afghanistan.