Although Iran claims that its nuclear program is exclusively for peaceful purposes, it has generated considerable concern that Tehran is pursuing a nuclear weapons program. Indeed, the UN Security Council has responded to Iran's refusal to suspend work on its uranium enrichment and heavy-water nuclear reactor programs by adopting several resolutions which imposed sanctions on Tehran. Despite this pressure, Iran continues to enrich uranium, install and operate additional centrifuges, and conduct research on new types of centrifuges.