Iran's ambassador to Belgium delivered a letter signed by Foreign Minister Manoucher Mottaki to the Brussels office of Javier Solana, the European Union's foreign-policy chief. Western diplomats declined to disclose details of either the letter or a phone conversation Solana had earlier in the day with Iran's chief nuclear negotiator, Saeed Jalili.

Both sides described Iran's response as positive.

Iranian news media said the two sides agreed to resume negotiations by the end of the Iranian month of Tir, which is July 21. No European official could confirm such a timeline.

"The conversation was constructive," Cristina Gallach, a spokeswoman for Solana, said in an e-mail. "All the noises are positive."

Iran faces the prospect of a fourth round of U.N. Security Council sanctions for refusing to stop its enrichment of uranium ore, a process that can produce fuel for a power plant or, if highly concentrated, explosive material for a nuclear bomb.

Iran insists its intentions are peaceful, but people in the West suspect otherwise. Backed by the United States and other world powers, Solana last month delivered a package of potential economic and political incentives meant to persuade Tehran to stop enriching uranium. Iran has offered its own package as a basis for compromise. But it does not mention the possibility of halting enrichment.

Iran is also considering a proposal from Solana under which it would stop adding new uranium-processing centrifuges and the West would refrain from pushing for sanctions during a six-week period before negotiations.

Fears of a military confrontation between Iran and the United States or Israel have pushed oil prices to record highs.

In an interview published yesterday, the head of Iran's elite Revolutionary Guard said his country would consider any attack on its nuclear installations the beginning of a larger confrontation.

"Any action against Iran will be considered the start of war," said Gen. Mohammad Ali Jaafari, according to the official Islamic Republic News Agency.

But while Iranian military officials have been painting dire scenarios in case of military action, diplomats have dramatically softened their rhetoric on the nuclear issue even as Iran refuses to budge on the enrichment issue.

Some critics in the United States say Iran is trying to run out the clock on the Bush administration without moving on enrichment, a strategy with which many Iranians concur.

Iran's mixture of inflammatory rhetoric and diplomatic finesse might reflect internal power struggles, with several conservative camps positioning themselves for 2009 presidential elections.

For years, Iran has insisted on uranium enrichment as a basic right. Backing down would expose conservative politicians such as President Mahmoud Ahmadinejad or a leading rival, parliamentary speaker Ali Larijani, to attacks by the hard-right news media and conservative religious groups, such as the Basij militia.