TEHRAN, (Reuters) – Iran’s chief nuclear negotiator said he hoped for “good and constructive” talks when he left Tehran on Friday to meet world powers in Geneva on the country’s disputed nuclear programme.

The United States is sending an envoy to the talks for the first time, seeking to underline to the Islamic Republic and others that Washington wants a diplomatic solution to the impasse.

That surprise U.S. move has raised hopes that the talks will help to defuse growing tensions over a nuclear programme which the West fears is a cover for making bombs. Tehran says it is aimed solely at generating electricity.

In a further indication of a possible thaw, Iranian Foreign Minister Manouchehr Mottaki raised the prospect of talks on restoring fractured relations between Iran and the United States. Washington has had no relations with Iran since 1980. “I think there may be talks on both the U.S. founding an interest preserving bureau in Iran and direct flights between the two countries,” Mottaki said during a visit to Ankara. He did not specify when and in what shape those talks could occur.

Chief nuclear negotiator Saeed Jalili was upbeat about the nuclear talks in Geneva on Saturday. “If they enter (negotiations) with a constructive approach and by avoiding previous mistakes, we can definitely have good and constructive negotiations,” Iranian media quoted Jalili as saying when asked about the U.S presence.

Senior U.S. diplomat Williams Burns will join European Union foreign policy chief Javier Solana and officials from Britain, France, Germany, Russia and China for the meeting.

The powers are seeking a more detailed Iranian response to their enhanced offer of financial and diplomatic incentives to halt secretive nuclear activity.

A senior Iranian official said the Geneva talks would be pivotal in deciding whether diplomacy could succeed. “This talks will clarify the fate of the negotiations. After the meeting, either negotiations will continue or it will fully stop,” the official told Reuters.

However, when asked whether it meant Iran was ready to freeze any expansion of its nuclear programme in return for the U.N. Security Council halting further sanctions measures against it, the source said “not at all”.

The U.N. has imposed three sets of sanctions on Iran over its nuclear programme.

Tensions with Iran have intensified, particularly since Tehran tested missiles last week, alarming Israel and pushing up oil prices. Washington responded to the tests by saying it would defend its allies against any possible attacks.

Oil prices fell 10 percent earlier this week on signs of an easing of tensions between Iran and the West and worries that high prices and a weaker U.S. economy will undermine demand.

Iran kept up its fiery rhetoric against the West on Friday.

“Playing with Iran is like playing with the lion’s tail,” influential Iranian cleric Ahmad Khatami told worshippers during Friday prayers in Tehran, broadcast live on state radio.

The Bush administration said it was not changing its stance that it will join full-blown negotiations with Iran only if Tehran first shelves uranium enrichment work, which can have both civilian and military uses.

Iran has repeatedly refused to stop its most sensitive nuclear work, as the six powers say it must do before formal talks can begin on the package of economic and other benefits.

Even for preliminary talks on the offer, they say Tehran must freeze any expansion of its nuclear programme in return for the U.N. Security Council halting further sanctions measures.

Washington would have the most to offer it in terms of relief from international political and economic sanctions, making U.S. engagement crucial to resolving the standoff, analysts say.

A British newspaper said on Thursday the United States would announce in the next month that it plans to establish a U.S. interest section in Tehran for the first time in 30 year.