US Secretary of State Condoleezza Rice said on Thursday it was time for Iran to change course and give up sensitive uranium enrichment work if it wanted to avoid becoming more isolated.
"It is time for Iran to change its tactics," Rice said just hours before EU foreign policy chief Javier Solana was due to meet Iran's nuclear negotiator, Ali Larijani, in Madrid.
"The international community is united on what Iran should do and that is to suspend (uranium enrichment) and demonstrate that it is not seeking a nuclear weapon," Rice added at a news conference on the sidelines of a women's empowerment conference in Vienna.
Her appeal to Iran came as Larijani made clear before talks with Solana that Tehran would not bow to demands to suspend enrichment over Western fears it is developing nuclear arms. Tehran says its nuclear program is for power generation.
Rice reiterated a US offer made one year ago that if Iran gave up its uranium enrichment work, which the West believes is aimed at building a nuclear bomb, then Washington was prepared to reverse decades of American policy and talk to Tehran on any issue.
"But that can't be done while Iran continues to pursue and to try and perfect technologies that are going to lead to a nuclear weapon. As I have said before, the question is not why won't we talk to Tehran but why won't Tehran talk to us," said Rice.
The US ambassador to Iraq met his Iranian counterpart in Baghdad this week in their most high-profile talks in nearly 30 years, but discussions were limited to security issues in Iraq and did not stray into the nuclear dossier.
Rice said if Iran was prepared to suspend its enrichment and joined negotiations with major powers, then UN Security Council activity would be suspended.
"While we have been willing to suspend so that there is a suspension of activity in the Security Council, Iran has not been willing to," she said.
Iran faces a third round of harsher sanctions for ignoring a UN Security Council deadline last week to stop enrichment.
Last week, the UNs atomic energy agency issued a report saying Iran was starting to enrich uranium in substantial amounts with 1,300 centrifuge machines and was likely to have 3,000 installed by mid-summer, laying the foundations for industrial production yielding large stockpiles of fuel convertible into material for atomic bombs.