Foreign Minister Manouchehr Mottaki said Teheran was open to discussions with Washington, which severed ties with Iran in 1980, but would not agree to a US precondition that it stop enriching uranium, the fuel used in nuclear reactors and a vital ingredient to developing atomic bombs.

“We will not give up our nation’s natural right (to enrichment), we will not hold talks over it. But we are ready to hold talks over mutual concerns,” Mottaki said.

World powers meet in Vienna on Thursday to try to agree on a plan to persuade Iran to halt nuclear work that could be a prelude to the development of nuclear weapons.

Washington’s offer was a policy shift that a senior US official said had won over Russia and China to pursuing sanctions against Teheran if it spurned the sweeteners.

He said that “if they (Iran) do not do so, there is also agreement that therefore we would have to proceed through the (UN) Security Council with a resolution and over time, depending on the Iranian response, move toward sanctions.

“What they’ve agreed is, if Iran does not accept this offer of negotiations, or accepts and then does not negotiate in good faith, we will return to the Security Council, we will get a resolution,” the official told reporters in Washington.

Mottaki said the US offer of talks, made by Secretary of State Condoleezza Rice, would not break the deadlock.

“Rice’s statement was not something new. This is what was said in her previous speeches and interviews. It lacked a logical and new solution to resolve Iran’s nuclear issue,” he said in Iran’s first official reaction.

Iran has consistently said it was ready for talks but would never abandon uranium enrichment completely.

Teheran says its nuclear fuel work is a non-negotiable civilian programme to generate electricity, not a covert quest for bombs as the West suspects.

Rice, announcing the US shift on Wednesday, said: “It’s time to know whether Iran is serious about negotiation or not.”

She said the move beefed up a “carrots and sticks” package for Iran whose essentials had been agreed with Britain, France and Germany ahead of Thursday’s gathering in Vienna and would be discussed further to pin down a consensus with Russia and China.

Foreign ministers from the five veto-holding, permanent powers on the Security Council along with Germany and EU foreign policy chief Javier Solana will aim to wrap up weeks of difficult negotiations on a viable strategy towards Iran.

US officials said Russia and China had come around to broad support for the “carrots and sticks” package drafted by the “EU3” -- France, Germany and Britain -- but details on how to balance the offer remained to be ironed out on Thursday.

Diplomats said the incentives were expected to encompass a light-water nuclear reactor and an assured foreign supply of atomic fuel so Iran would not need to enrich uranium itself.

Sanctions could entail visa bans and a freeze on assets of senior Iranian officials before resorting to trade measures.

Big stick lowered for now

Rice reiterated that a last-resort military option, should talks or sanctions prove futile, remained on the table.

But Washington, angling for firm Russian support, had accepted language in a proposed Council resolution to underpin the offer that would rule out an immediate threat of military strikes on Teheran, US and European officials said.

Western leaders had wanted the resolution to designate Iran a “threat to international peace and security”, a legal pathway to use of force applied in 2003 to topple Iraq’s Saddam Hussein.

But Russia and China see no such danger and oppose any automatic penalty trigger until diplomatic opportunities have been exhausted. Nuclear analysts say Iran is three to 10 years away from enriching enough uranium to make a nuclear weapon.

The Russian and Chinese ambassadors to the United Nations welcomed the US talks offer. But Beijing’s envoy urged the United States not to load the proposal with preconditions.

France, Britain and Germany, which have led talks with Iran, said Teheran would face more credible pressure to compromise.

“We can only hope that those in charge in Teheran understand the scope of this announcement and will react accordingly,” said German Foreign Minister Frank-Walter Steinmeier.