The United States used an international meeting on Afghanistan to make an unusual direct diplomatic overture to Iran.

U.S. Secretary of State Hillary Rodham Clinton said the Americans delivered a letter to the Iranians at Tuesday''s meeting in The Hague. The letter asks Iran to help resolve the cases of three detained or missing Americans.

The cases, and the U.S. position on them, were already known. What''s new is the Obama administration''s choice to approach Iran directly, instead of through a go-between. The two countries have had no formal diplomatic ties for nearly three decades.

Clinton said she sent Iran a direct letter concerning three U.S. citizens unable to return from Iran: Robert Levinson, Roxana Saberi, Esha Momeni. Their return would be a humanitarian gesture, the letter said.

Levinson, a retired FBI agent from Coral Springs, Fla., was last seen on Iran''s Kish Island on March 8, 2007. He disappeared in Iran while investigating cigarette smuggling for a client of his private security firm.

The Iranian government has said Saberi was imprisoned for doing reporting work in the country after her press credentials expired. Her parents found out about her arrest in a brief phone call from her Feb. 10. Saberi grew up in Fargo and is a dual citizen of the U.S. and Iran and has reported for several news organizations.

Momeni, a dual U.S. and Iranian national, was visiting Tehran to research a master''s thesis on the women''s rights movement in Iran. Momeni, born in Los Angeles, was arrested Oct. 15 on a traffic violation.