The new US envoy to the United Nations says Barack Obama's administration will make Iran's nuclear plans a diplomatic priority and pursue direct talks.
Susan Rice told reporters she looked forward to "vigorous diplomacy that includes direct diplomacy with Iran".
Under George W Bush, there were no direct US nuclear talks with Iran.
The UN has urged Tehran to halt uranium enrichment, amid fears it could be used for military purposes. Iran says its nuclear programme is entirely peaceful.
In the run-up to his inauguration last week, Mr Obama promised a "new approach" in the dispute.
Last month he called for "tough but direct diplomacy", offering Iran economic incentives to end its nuclear programme or face tougher sanctions.
Iran dismissed the move as "unacceptable".
Ms Rice was speaking after presenting her credentials to UN Secretary General Ban Ki-moon.
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