Following are details of sanctions imposed on Iran in recent years by the United States, the United Nations and the European Union.
* U.S. SANCTIONS:
-- Initial sanctions imposed after Iranian students stormed the U.S. embassy and took diplomats hostage in 1979. Iranian products cannot be imported into the United States apart from small gifts, information materials, foodstuffs and some carpets.
-- In 1995, President Bill Clinton issued executive orders preventing U.S. companies from investing in Iranian oil and gas and trading with Iran. Tehran has looked for other customers.
-- The same year, Congress passed a law requiring the U.S. government to impose sanctions on foreign firms investing more than $20 million a year in Iran's energy sector. It was extended for five years in September 2006. No foreign firms have yet been penalized, although many have curtailed operations in Iran.
-- In October 2007, Washington imposed sanctions on three Iranian banks and branded the Revolutionary Guards a proliferator of weapons of mass destruction. The Treasury has since added numerous other Iranian banks to its blacklist.
-- The Treasury has identified about 20 petroleum and petrochemical companies as being under Iranian government control, an action that put them off-limits to U.S. businesses under the trade embargo.
-- Congress approved tough new unilateral sanctions on June 24, 2010 aimed at squeezing Iran's energy and banking sectors, which could also hurt companies from other countries doing business with Tehran.
-- The 2010 law imposes penalties on firms that supply Iran with refined petroleum products worth more than $5 million over 12 months. Firms can be banned from the U.S. financial system or denied U.S. contracts. It also effectively deprives foreign banks of access to the U.S. financial system if they do business with Iranian banks or the Revolutionary Guards.
-- In February 2011, Bank Refah was sanctioned for facilitating the purchase of millions of dollars worth of missiles and tanks by Iran's Defense Ministry.
-- In May, the U.S. blacklisted its 21st Iranian state bank, the Bank of Industry and Mine, as a proliferator of weapons of mass destruction for handling transactions on behalf of two previously sanctioned institutions, Bank Mellat and Europaeisch-Iranische Handelsbank.
-- It also announced new sanctions on Venezuela's state oil company PDVSA and six other smaller oil and shipping firms for engaging in trade with Iran in violation of the U.S. ban, prompting fury and warnings from Hugo Chavez's government.
-- On June 11, it announced new sanctions applicable to the Islamic Revolutionary Guard Corps, the Basij Resistance Force, Iran's Law Enforcement Forces and its commander, Ismail Ahmadi Moghadam. The sanctions freeze any of the targets' assets under U.S. jurisdiction and bar U.S. persons and institutions from dealing with them.
* EU SANCTIONS:
-- The EU has imposed visa bans on senior officials such as Revolutionary Guards chief Mohammad Ali Jafari, former Defense Minister Mostafa Mohammad Najjar and former atomic energy chief Gholamreza Aghazadeh, and on nuclear and ballistic experts.
-- Britain announced last October it was freezing business ties with Bank Mellat and Islamic Republic of Iran Shipping Lines (IRISL), both of which have previously faced sanctions from the United States.
-- New EU measures approved on July 26, 2010, said European airports would bar cargo flights to or from Iran except those in which limited amounts of cargo were carried on passenger planes.
-- On August 12, 2010 the EU toughened its sanctions against Tehran, including banning the creation of joint ventures with enterprises in Iran that are engaged in the oil and natural gas industries and any subsidiary or affiliate under their control.
-- Member states must prohibit the provision of insurance and re-insurance to the government of Iran. The sale, purchase, brokerage or assistance with the issuance of public or public-guaranteed bonds by the Iranian government, central bank or Iranian banks is banned.
-- The import and export of arms and equipment that could contribute to uranium enrichment or have a "dual use" is banned.
-- The sanctions forbid the sale and supply or transfer of energy equipment and technology used by Iran for refining, liquefying natural gas, exploration and production. The EU expects the effects of the sanctions to increase over time as existing parts wear out.
-- The transfer of funds over 40,000 euros will require prior authorization from the member state concerned. Sums of more than 10,000 euros not related to foodstuffs or healthcare and medical equipment will require notification.
-- In May 2011, EU foreign ministers significantly extended its sanctions and agreed to add more than 100 new entities to a list of companies and people affected by sanctions including those owned or controlled by the IRISL. Among the shipping companies targeted by the EU were Safiran Payam Darya Shipping Lines, which it said took over IRISL's bulk services and routes and used vessels previously owned by IRISL.
-- EU diplomats said the May 23 sanctions list included German-based EIH bank, which specializes in business in Iran.
* U.N. SANCTIONS:
-- The Security Council has imposed four sets of sanctions on Iran, in December 2006, March 2007, March 2008 and June 2010.
-- The first covered sensitive nuclear materials and froze the assets of Iranian individuals and companies linked with the nuclear program. It gave Iran 60 days to suspend uranium enrichment, a deadline ignored by Iran.
-- The second included new arms and financial sanctions. It extended an asset freeze to 28 more groups, companies and individuals engaged in or supporting sensitive nuclear work or the development of ballistic missiles, including the state-run Bank Sepah and firms controlled by the Revolutionary Guards.
-- The third increased travel and financial curbs on individuals and companies. It expanded a partial ban on trade in items with both civilian and military uses to cover sales of all such technology to Iran, and added 13 individuals and 12 companies to the list of those suspected of aiding Iran's nuclear and missile programs. In September 2008, the Security Council unanimously adopted a resolution again ordering Iran to halt enrichment. Iran again disregarded the order.
-- A Security Council resolution passed on June 9, 2010, called for measures against new Iranian banks abroad if a connection to the nuclear or missile programs was suspected, as well as vigilance over transactions with any Iranian bank, including the central bank.
-- It expanded a U.N. arms embargo against Tehran and blacklisted three firms controlled by Islamic Republic of Iran Shipping Lines and 15 belonging to the Islamic Revolutionary Guard Corps. The resolution called for setting up a cargo inspection regime similar to one in place for North Korea.
-- Annexed to the draft resolution was a list of 40 companies to be added to an existing U.N. blacklist of firms.
(Writing by David Cutler, London Editorial Reference Unit; editing by Mark Heinrich)