IRANIAN OFFICIALS ruled out any freeze in uranium enrichment yesterday at the start of talks over Tehran's nuclear programme, attended for the first time by a senior US diplomat.

"Any kind of suspension or freeze is out of the question," said an Iranian official rejecting the main condition set by the United States and other major powers for formal negotiations to end the long-running dispute.

The high-level US participation in the one-day meeting in Geneva, together with Iranian comments playing down the likelihood of an attack by the United States and Israel, had raised hopes of progress and helped ease record oil prices.

But the optimism was tempered by US insistence that, despite the presence of its envoy, William Burns, real negotiations cannot begin until Iran has frozen sensitive nuclear work, a step Tehran has repeatedly ruled out.

"That remains the US position and it will continue to be the US position," US secretary of state Condoleezza Rice told a news conference in Washington.

Iran's ambassador to Switzerland said Iran would not accept freezing enrichment. "It is not in Iran's agenda to discuss this issue," Keyvan Imani said.

"As our supreme leader Ayatollah Ali Khamenei clearly said, our path is very clear: we are not going to abandon our rights."

Khamenei said on Wednesday Iran was ready to negotiate, but showed no sign of backing down on the Islamic Republic's refusal to halt atomic activities.

The Iranian comments dampened hopes raised by upbeat statements ahead of the talks, which Iranian foreign minister Manouchehr Mottaki portrayed as "positive and constructive".

"Today's meeting might continue with several others so that the viewpoints of all sides can be put on the table, so that we reach agreement," he said.

He did not elaborate what he meant by agreement, but added that he hoped the talks would pave the way for agreeing on "a modality and a framework" for further negotiations.

Iran's chief nuclear negotiator, Saeed Jalili, also spoke of his "positive intentions" as he arrived in Geneva on Friday for the talks with officials from the United States, Russia, China, France, Britain and Germany - the so-called sextet.

Iran, the world's fourth-largest oil producer, rejects suspicions that it wants the atom bomb, saying the aim of the nuclear programme is to generate electricity so that it can export more oil and gas.

Western diplomats say they want the talks to clarify Iran's response to an offer, delivered last month, of technical and commercial incentives to suspend uranium enrichment.

Tension has intensified since Tehran tested missiles earlier this month, alarming Israel and unsettling energy markets on fears that conflict could disrupt oil supplies.