May 27 (Reuters) - South Korea on Wednesday became the 95th member of the Proliferation Security Initiative, an ad hoc alliance of states working to stop shipments of weapons of mass destruction.

Following are key facts about the PSI, touted by many experts as a possible tool to rein in North Korea's nuclear weapons ambitions and proliferation of missiles and other illicit weapons.

MISSION - To stop trafficking of weapons of mass destruction, their delivery systems and related materials to and from states and non-state actors of proliferation concern through voluntary actions by states consistent with national and international laws and legal frameworks.

HISTORY - Launched by U.S. President George W. Bush on May 31, 2003, based on U.S. National Strategy to Combat Weapons of Mass Destruction issued in December 2002 as part of a U.S. response to threats highlighted by the Sept. 11 attacks in 2001.

EXERCISES - More than 30 exercises were held between September 2003 and January 2008. Some were led by the United States but most were directed by other PSI participating nations.

PROMINENT MEMBERS - Argentina, Australia, Britain, Canada, Denmark, France, Germany, Greece, Iraq, Israel, Italy, Japan, Mongolia, The Netherlands, New Zealand, Norway, Russia, Saudi Arabia, Singapore, South Korea, Spain, Sweden, Switzerland, Turkey, Ukraine, United States, Yemen. (Sources: U.S. State Department, Pentagon) (Reporting by David Morgan and Paul Eckert; Editing by John O'Callaghan)

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