President Obama makes a direct appeal to Iran's leaders
Iran has given a cautious welcome to US President Barack Obama's offer of "a new beginning" in relations, but said the US had to change its behaviour.
An adviser to Iranian President Mahmoud Ahmadinejad said Washington must reverse its support for Israel and end sanctions against Iran.
The adviser, Ali Akbar Javanfekr, also said the US had to apologise to Iran for its past actions.
Mr Obama's offer came in a direct video address to mark the Iranian New Year.
In the message, Mr Obama said he was seeking engagement with Iran that was "honest and based on mutual respect".
"My administration is now committed to diplomacy that addresses the full range of issues before us," he said.
The address was distributed to news outlets in Iran with subtitles in Farsi, and posted on the White House website.
The unprecedented approach is a dramatic departure from the policies of the Bush administration, which described Iran as part of the "axis of evil", the BBC's Jonathan Beale in Washington says.
But in separate Nowruz (Persian new year) messages to the Iranian people, neither Supreme Leader Ayatollah Ali Khamenei nor President Ahmadinejad mentioned Mr Obama's speech.
Relations between Iran and the US have been strained over Tehran's controversial nuclear activities.
'Friendly hand'
Reacting to Mr Obama's message, Mr Javanfekr said the US had to recognise its past mistakes if it wanted to engage Iran.
He said if the US did so, Iran would not turn its back.
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"
"By fundamentally changing its behaviour America can offer us a friendly hand," he told Reuters news agency.
"Unlimited sanctions which still continue and have been renewed by the United States are wrong and need to be reviewed," he said.
"Supporting Israel is not a friendly gesture and the New Year is an opportunity for the United States to change this policy."
The US fears Iran's uranium enrichment programme is a cover to build atomic weapons, a charge Iranian officials deny.
In his Nowruz address, Ayatollah Khamenei said world powers had been convinced they could do nothing to halt the progress Iran was making on its nuclear programme.
Mr Obama, like his predecessor George W Bush, wants Iran to abandon its uranium enrichment programme, but is trying to build up diplomatic capital before confronting the issue, says BBC diplomatic correspondent Jonathan Marcus.
Meanwhile, Israeli President Shimon Peres issued a rare Nowruz greeting of his own to the Iranian people, broadcast in Iran by the Farsi-language service of the Voice of Israel radio station.
But in an interview due to be broadcast on Monday, Mr Peres will take a tougher line, predicting that Iranians will eventually topple their leaders because they do not serve the people.
Warning
EU foreign policy chief Javier Solana described Mr Obama's appeal as "very constructive" and urged Tehran to pay close attention to it.
In the message, Mr Obama said he wanted "to speak directly to the people and leaders of the Islamic Republic of Iran".
What is the new administration actually offering, that George Bush didn't?
He said his administration was committed "to pursuing constructive ties among the United States, Iran and the international community".
"With the coming of a new season, we're reminded of this precious humanity that we all share. And we can once again call upon this spirit as we seek the promise of a new beginning," the message said.
But Mr Obama warned: "This process will not be advanced by threats. We seek instead engagement that is honest and grounded in mutual respect.
"The United States wants the Islamic Republic of Iran to take its rightful place in the community of nations. You have that right - but it comes with real responsibilities."
'Axis of evil'
Earlier this year, President Obama said he was looking for "openings that can be created where we can start sitting across the table face-to-face" with Iran.
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 Ayatollah Khamenei before the Iranian elections this summer.
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