Iran sent mixed messages Thursday about its nuclear agenda: The ruling cleric vowed not to give up the atomic program — calling it more important than oil revenues — but the president said Tehran is ready to negotiate on resolving the standoff.

Both comments came as the United States and Europe, during the board meeting of the U.N. nuclear watchdog in Vienna, Austria, urged Iran to abandon the secrecy surrounding its nuclear activities and to freeze uranium enrichment. Washington warned that continued defiance could result in tough measures by the U.N. Security Council.

In Tehran, Supreme Leader Ayatollah Ali Khamenei called the dispute over Iran's efforts to enrich uranium an unwarranted "Western outcry" and said the nation would not succumb to Western pressure to stop.

Speaking to Iranian nuclear experts, he said achieving nuclear technology was more important than mining for oil in Iran, where oil revenue makes up some 80 percent of foreign-exchange earnings.

"Let me tell you, the importance of achieving and using nuclear energy is higher than oil exploration for our country," state-run television reported him as saying.

However, President Mahmoud Ahmadinejad, in talks in Shanghai, China with Russian President Vladimir Putin, said Iran was ready to enter negotiations on an incentives package by the U.N. powers designed to encourage it to relinquish its nuclear fuel enrichment program.

"The Iranian side responded positively to the six-nation proposal for a way out of the crisis," Putin told reporters afterward. He said "Iran is ready to enter negotiations" and that he hoped that it would soon set a date for the start of talks.

Ehsan Jahandideh, a member of the Iranian president's delegation in Shanghai for a regional summit, confirmed Ahmadinejad's remarks.

The proposal by the five permanent U.N. Security Council members, plus Germany, offers Tehran a package of incentives in return for talks. It calls for Iran to suspend uranium enrichment for the duration of any negotiations.

It also sets out the priority of a long-term moratorium on enrichment until the international community is convinced that Tehran's nuclear aims are peaceful — as it claims they are. Iran says it seeks to generate nuclear energy, not weaponry.

In Washington, White House press secretary Tony Snow, asked about the Russians and Chinese work with Iran, said the six nations are united in the goal of getting Tehran to suspend uranium enrichment and reprocessing activities.

"I fully expect them to try any number of ways of trying to shape the debate," he said. "But the precondition is clear. Everybody's agreed on it.

Russia has been Iran's staunchest backer in the dispute with the West, followed by China. Ahmadinejad meets Chinese President Hu Jintao on Friday. The United States, France and Britain are also permanent security council members.

On Sunday, Iran's Foreign Ministry said the government found parts of the Western incentives package "acceptable," but said other parts should be removed. The ministry spokesman did not elaborate, but his comments reflected Iran's intention to seek changes in the offer.

The package already includes significant concessions by the United States, pulling back from demands that Iran scrap its enrichment program as an initial condition for negotiations and seeking a suspension instead. However, it also contains the implicit threat of U.N. sanctions if Iran remains defiant.

When presented with the proposal's details last week, Iran said they contain "positive steps" but also ambiguities, which it said had to be cleared up in further talks.

EU foreign policy chief Javier Solana, who presented the offer to Tehran, said he expected a reply within "weeks."

Iran has consistently refused to give up enrichment, a process that can produce either fuel for a nuclear reactor or the material for a nuclear warhead. Iran insists it has the right to develop enrichment — though it has signaled it might compromise on large-scale enrichment.

In Vienna, Francois-Xavier Deniau, France's chief delegate to the 35-nation board meeting of the International Atomic Energy Agency, criticized Iran for a lack of cooperation with the agency's probe of suspicious plutonium experiments and other activities that could be linked to a weapons program.

"Cooperation with the agency has been reduced to almost nothing these last few months and ... numerous important questions remain to be resolved," said the statement.

Separately, U.S. chief delegate Gregory L. Schulte said "Iran continues to withhold cooperation with the IAEA on almost every outstanding issue." He urged Tehran to accept the incentives package, warning that refusal could bring to bear "the weight of the Security Council."

In a statement to the IAEA board, chief Iranian representative Ali Ashgar Soltanieh warned against "the use of the language of threat" in trying to persuade Tehran to cooperate. He said Iran was ready to negotiate only "without any precondition" — an apparent rejection of suspending enrichment as a condition for talks.

Separately, he told reporters that enrichment was Iran's "inalienable right," but said his country was "determined to ... find a negotiated solution."

The United States said late last month that it was ready to break with decades of policy and talk to Iran directly in a multinational framework on its nuclear program. Russia and China also seem ready to join.

Still, China, Russia and possibly Germany might push to allow Iran some tightly controlled and small-scale enrichment rather than see talks founder, diplomats said. Russia and China also might balk at enforcing selective U.N. sanctions on Iranian officials and activities.