The U.N. Security Council first imposed sanctions against Iran in December 2006 and has been ratcheting up the punitive measures since then in hopes of pressuring the government to suspend enrichment and start negotiations on its nuclear program _ which it has refused to do.
The council has acted in response to reports from the International Atomic Energy Agency, which is expected to release new details this week indicating possible secret work by Iran to develop nuclear weapons. It could lead to new sanctions.
Here is a rundown of the four sanctions resolutions adopted thus far:
_ December 2006: The council ordered all countries to stop supplying Iran with materials and technology that could contribute to its nuclear and missile programs. It also ordered countries to freeze the assets of 10 key Iranian companies and 12 individuals related to those programs.
_ March 2007: The council banned Iranian arms exports and ordered countries to freeze the assets of 28 additional individuals and organizations involved in Iran's nuclear and missile programs. It called for voluntary restrictions on travel by the individuals subject to sanctions, on arms sales to Iran, and on new financial assistance or loans to the Iranian government.
_ March 2008: The council banned all countries from trading with Iran in goods that have both civilian and military uses. It authorized inspection of cargo suspected of containing banned items on planes and ships that are owned or operated by Iran Air Cargo and Islamic Republic of Iran Shipping Line. It authorized financial monitoring of Bank Melli and Bank Saderat, called on all countries "to exercise vigilance" in entering into new trade commitments, and froze the assets of 12 additional companies and 13 individuals.
_ June 2010: The council banned Iran from pursuing "any activity related to ballistic missiles capable of delivering nuclear weapons," barred Iranian investment in activities such as uranium mining, and prohibited Iran from buying several categories of heavy weapons. It called on all countries to cooperate in the inspection of suspect cargo and to block financial transactions and ban the licensing of Iranian banks if they have "reasonable grounds" to believe these activities could contribute to Iranian nuclear activities.
The council also imposed sanctions on 40 Iranian companies and organizations. It added one individual to the previous list of 40 Iranians subject to an asset freeze and banned travel for all of them.
Oil exports, the lifeblood of Iran's economy, are not affected by sanctions because of opposition from Russia and China, which have veto power on council decisions.