President Hassan Rowhani said Tuesday Iran was ready for "serious" talks on its nuclear programme without delay and that US calls for tougher sanctions showed a lack of understanding.
Addressing his first news conference since taking office on Saturday, Rowhani said he would not surrender Iran's rights but that he wanted to allay Western concerns.
"As the president of the Islamic republic, I am announcing that there is the political will to solve this issue and also take into consideration the concerns of the other sides," he said.
"We are the people of interaction and talks, with seriousness and without wasting time, if the other sides are ready."
Rowhani headed Iran's nuclear negotiating team under reformist president Mohammad Khatami in the early 2000s, and Western leaders have expressed hope his election could herald a more constructive approach in the protracted talks.
The hardline policies of his firebrand predecessor, Mahmoud Ahmadinejad, prompted crippling EU and US sanctions against Iran's oil and banking sectors that he has vowed to seek to relax.
Rowhani said there could be no surrender of the right to the peaceful use of nuclear energy that Iran claims under the Non-Proliferation Treaty.
"Iran's peaceful nuclear programme is a national issue... we will not give up the rights of the Iranian people," he said.
"We will preserve our rights based on the international regulations."
He also stressed that Iran would not give up uranium enrichment -- the sensitive nuclear activity at the heart of Western concerns, which Iran suspended when Rowhani was chief negotiator a decade ago.
"In Iran, nobody has said we will give up uranium enrichment, no one and at no time," he said.
And he reiterated his insistence that Iran would not negotiate under the threat of economic sanctions or military action.
In Washington, State Department spokeswoman Jen Psaki said there were still steps Iran needed to take "to meet their international obligations and find a peaceful solution to this issue."
"The ball is in their court," she added.
"If there's a credible proposal and actions that are taken, again the United States will be a willing partner. But we're not quite there yet," said Psaki.
-- 'Contradictory messages' --
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Rowhani had earlier hit out at what he termed "contradictory messages" from Washington.
The White House has said that it would be a "willing partner" in genuine talks, but the US Senate has urged tougher sanctions.
"Recent declarations from the White House show that some US officials do not have a correct and realistic assessment of the situation here and the message that the Iranian people gave in the election," Rowhani said.
"They are still sending contradictory messages," he said, adding: "We care about the US response in deeds, not in words."
On Sunday, the White House said Iran would find the United States a "willing partner" if Rowhani is prepared to engage substantively and seriously on its nuclear programme.
In a message congratulating Rowhani on his inauguration, the White House said it "presents an opportunity for Iran to act quickly to resolve the international community's deep concerns over Iran's nuclear programme."
Western governments suspect Iran's nuclear programme is cover for a drive for a weapons capability, an ambition Tehran strongly denies.
Rowhani took particular issue with a letter signed by 76 US Senators -- just over three-quarters of the total -- calling for tougher US sanctions, even as he promised more constructive engagement.
He charged that the letter was the work of a "foreign country" and its supporters in the United States, a clear allusion to Iran's arch-foe Israel.
Russia, too, strongly criticised the US senators' sanctions call, saying it was in the world's interests to respond positively to Rowhani's talks offer.
"I think these ideas contradict the fundamental interests of the international community," Foreign Minister Sergei Lavrov said of the letter.
"These are dangerous games and we hope reason will prevail."
Lavrov said it was "extremely important" for the major powers to support the new approach from the Iranian leadership and to hold fresh talks as soon as possible.
But Israel -- which has the Middle East's sole, if undeclared, nuclear arsenal -- called for "increased pressure" on the Iranian regime, saying that it was the only language that it understood.
"The only thing that has worked in the last two decades is pressure. And the only thing that will work now is increased pressure," Prime Minister Benjamin Netanyahu told a delegation of 36 visiting US Congressmen.
Both Israel and the United States have refused to rule out resorting to military action to prevent Iran acquiring a a nuclear weapons capability, but Washington has said it wants to exhaust all diplomatic avenues first.