FACTBOX: Sanctions on Iran and what could follow

(Reuters) - World powers failed to reach a decision on Saturday on further sanctions to punish Iran for its disputed nuclear program, a French diplomat said.

The United States and European allies want a third round of U.N. sanctions on Iran for failing to meet U.N. demands to halt sensitive atomic work, which the West says is aimed at building atomic bombs despite Tehran's denials.

Russia and China, both veto-wielding members of the U.N. Security Council, have resisted such a move.

Following are details about what sanctions have been imposed on Iran by the U.N. Security Council and United States, and also what another U.N. resolution could involve:

WHAT SANCTIONS HAVE BEEN IMPOSED ON IRAN?

* UN SANCTIONS:

-- The U.N. Security Council has imposed two sets of mild sanctions on Iran, the first resolution was passed in December 2006 and a second approved in March 2007.

-- Both sets of sanctions were approved unanimously after wrangling between the five permanent Council members -- the United States, France, Britain, China and Russia -- plus Germany, in the so-called P5+1.

-- THE FIRST ROUND: The sanctions covered sensitive nuclear materials and froze the assets of Iranian individuals and companies associated with the program. It gave Iran 60 days to suspend uranium enrichment, a process which can be used to make nuclear power plant fuel or bomb material. Iran did not stop.

-- THE SECOND ROUND: The resolution in March included new arms and financial sanctions. It extended an asset freeze to 28 additional groups, companies and individuals engaged in or supporting sensitive nuclear activities or development of ballistic missiles.

-- State-run Bank Sepah and commanders and firms controlled by Iran's Revolutionary Guards, including commanders of one its units, the Qods Force, were included on the list.

-- The resolution invoked Chapter 7, Article 41 of the U.N. Charter, which makes most of its provisions mandatory but excludes military action. Iran again failed to meet a 60-day deadline to halt enrichment.

* U.S. SANCTIONS:

-- Iran has imposed various sanctions on Iran since 1979 after radical Iranian students stormed the U.S. embassy in Tehran and took U.S. diplomats hostage.

-- The measures prohibit most trade between the United States and the Islamic Republic.

-- In 1995, then U.S. President Bill Clinton issued executive orders preventing U.S. companies from investing in Iranian oil and gas and trading with Iran.