The letter was sent via the Swiss Embassy in Tehran since the United States and Iran have no diplomatic relations.
U.S. officials have been quoted as saying the letter may have been sent to influence a debate at the United Nations Security Council on a proposed resolution that would obligate Iran to halt uranium enrichment. Russia and China continue to oppose any references in the draft to possible sanctions or military force against Iran.
An Iranian government spokesman, Gholam-Hossein Elham, said the letter proposed "new solutions" for resolving international problems.
(compiled from agency reports)