President Obama makes a direct appeal to Iran's leaders
US President Barack Obama has offered "a new beginning" of engagement with Tehran in an unprecedented direct video message to the Iranian people.
"My administration is now committed to diplomacy that addresses the full range of issues before us," Mr Obama said.
An advisor to Iran's president welcomed Mr Obama's message but said Washington had to fundamentally change policy.
Relations between Iran and the US have been strained over Tehran's controversial nuclear activities.
The US fears Iran's uranium enrichment programme is a cover to build atomic weapons, a charge Iranian officials deny.
Mr Obama, like his predecessor, wants Iran to abandon its uranium enrichment programme, but is trying to build up diplomatic capital before confronting the issue, says the BBC's diplomatic correspondent Jonathan Marcus.
EU foreign policy chief Javier Solana described Mr Obama's appeal as "very constructive" and urged Teheran to pay close attention to it.
Paul Reynolds, World affairs correspondent
President Barack Obama's video message is an imaginative start to his attempt to improve relations - but huge obstacles remain.
In diplomacy such efforts at overcoming major differences sometimes end simply in defining those differences more sharply.
These issues were not directly mentioned by Mr Obama but this is what he is referring to:
Iran to give up uranium enrichment and accept international offers to provide fuel for nuclear power
Iran to stop arming Hezbollah in Lebanon and Hamas in Gaza
Iran to help in achieving peace in Afghanistan and Iraq
Iran to stop threatening Israel.
Iran will want the following:
Acceptance of its right to enrich uranium
An end to UN sanctions
An end to US sanctions
An end to America's "colonialist attitudes"
However, Mr Obama acknowledged in his message on Thursday that it would not be easy to overcome "the old divisions".
Mr Obama has talked of engagement with Iran but has not made clear how that might take place.
Shortly after coming to office in January, he said "if countries like Iran are willing to unclench their fists, they will find an extended hand from us".
But earlier this month he extended sanctions against Iran for a year, saying it continues to pose a threat to US national security.
In another possible move towards engagement, the state department is said to be considering an overture in the form of a letter to Iran's Supreme Leader Ayatollah Khamenei before the Iranian elections this summer.
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