U.N. Secretary-General Kofi Annan has cautioned Iran to step back from its aggressive stance and reassure the world that its nuclear program is peaceful. Meanwhile, U.N. diplomats are speaking of a shift in the tone of discussions on Iran, from confrontation to engagement.

Secretary-General Annan Wednesday expressed optimism that efforts to find a diplomatic solution to Iran's nuclear ambitions are being intensified.

He spoke shortly after U.S. Secretary of State Condoleezza Rice said Western governments would wait a few weeks before pushing for further Security Council action on Iran's suspect nuclear program.

But on a day when Iranian President Mahmoud Ahmedinejad accused Western nations of hypocrisy, and called their expressions of concern about Tehran's nuclear program a "big lie", Mr. Annan warned Iran to cool its rhetoric.

"I think it is important that the Iranians remain open and that they back away from this aggressive posture, and be open to discussions," said Kofi Annan. "I think that no one is saying that they are not entitled to peaceful use of nuclear energy. But they have a responsibility to communicate and to show that their intention is peaceful."

Meanwhile, Russia's Ambassador Vitaly Churkin hailed what he called a "change of mood" during this weeks' ministerial-level talks on Iran. Churkin spoke of an evolution in the tone of diplomacy since last week, when European nations asked the Security Council to invoke Chapter seven of the U.N. charter, legally requiring Tehran to halt uranium enrichment.

"You will recall that when this was presented by the French and the British, the words you heard, Chapter Seven, and threat to peace, and how many days they will be given to obey what is going to be in the resolution, and then diplomacy in its quiet way did its job, because some of you may not have noticed but the mood has changed completely," said Vitaly Churkin.

Churkin said this week's ministerial talks in New York had been marked by a turn away from the earlier tone of confrontation to one of engagement.

"As a result of what has been achieved so far is we have reason to say to Iran that they should not be looking at the process in any kind of a confrontational mode, because the process is not confrontational to them," he said.

The new mood was reflected in the comments of Washington's U.N. Ambassador John Bolton. Earlier, he had pushed for prompt passage of the British-French draft resolution, with a short deadline for Iranian compliance.

Wednesday, Bolton expressed skepticism about whether Iran would accept a proposed European package of incentives in return for suspending uranium enrichment. But he suggested the idea was worth a try in the interest of maintaining unity among the five permanent Security Council members.

"I think the possibility of Perm five unity is important," said John Bolton. "That's what this initiative is designed to undertake. We'll see what happens in terms of putting the package together, and based on whether the Iranians accept the package, that will tell us what we'll do here."

European diplomats hope to have their package of energy and trade incentives ready by next Monday. It will be presented to top diplomats of the five permanent Council members and Germany in London later in the week. In the mean time, the draft resolution on Iran is being put aside to allow time for diplomacy to work.