Since the seizure of U.S. hostages in Iran following the 1979 revolution, the U.S. government has imposed a succession of economic penalties against the Islamic Republic. The complexity and severity of these sanctions intensified following Iran's resumption of a uranium enrichment program in 2006. However, there are a variety of ways to provide extensive sanctions relief should there be a deal placing long-term restrictions on Iran's nuclear activities.
The November 24, 2013 Joint Plan of Action (JPA) between Iran and the "P5+1" countries (the United Staets, Britain, France, Germany, Russia, and China) pledges Iran comprehensive international sanctions relief if a final settlement is reached on its nuclear program. The JPA does not assert that the United States is the sole source of existing sanctions. However, U.S. sanctions are key to sanctions relief because many U.S. sanctions penalize foreign countries and companies that conduct specified transactions with Iran.
The JPA does contain several ambiguities with respect to sanctions relief. It states that a comprehensive deal would be implemented in reciprocal steps – a reference to U.S. official statements that the promised sanctions relief would not be provided immediately, but rather phased in as Iran fulfills its commitments under any negotiated solution. Furthermore, the JPA promises Iran lifting of "sanctions related to Iran's nuclear program" – leaving it to the negotiations to decide which sanctions are "nuclear related" and which might relate only to Iran's support for terrorist organizations, its human rights record, or other issues.
See full text at the Atlantic Council: Easing U.S. Sanctions on Iran