Iran's president has written to President Bush proposing "new solutions" to their differences, a spokesman in Tehran said Monday.

Government spokesman Gholam-Hossein Elham said the letter would be the first in 27 years from an Iranian leader to an American president.

The letter was sent via the Swiss Embassy, which hosts a U.S. interests section in Tehran, Elham told a news conference.

The United States has had no diplomatic relations with Iran since the 1979 storming of the American Embassy in Tehran.

In the letter, Iranian President Mahmoud Ahmadinejad proposes "new solutions for getting out of international problems and current fragile situation of the world," Elham said.

Elham did not mention the nuclear dispute ¡ª the main obstacle between Washington and Tehran. The United States is leading Western efforts to pass a U.N. Security Council motion censuring Iran for refusing to cease enrichment of uranium.

On Sunday, Ahmadinejad renewed Iran's threat to withdraw from the Nuclear Nonproliferation Treaty if the Security Council imposes sanctions on Tehran.

The United States is backing efforts by Britain and France to win Security Council approval for a U.N. resolution that would threaten possible further measures if Iran does not suspend uranium enrichment ¡ª a process that can produce fuel for nuclear reactors to generate electricity or material for nuclear warheads.

The Western nations want to invoke Chapter 7 of the U.N. Charter that would allow economic sanctions or military action, if necessary, to force Iran to comply with the Security Council's demand that it cease enrichment.

But Russia and China, the other two veto-holding members of the Security Council members, oppose such moves.

Iran claims its nuclear program is strictly for generating electricity and that it requires enrichment to be self-reliant in fuel for nuclear reactors.

But the United States and France believe that Iran is secretely developing nuclear weapons ¡ª a charge Iran denies.