Iranian and international wire reports from Tehran said that Iran had sent a letter to EU foreign policy chief Javier Solana on Tuesday, the deadline that Britain had given Iran to respond positively to the incentive package or face tougher U.N. sanctions.

Tehran's official media did not mention the letter, first leaked by the unofficial Iranian Fars news agency, while Solana's aides privately said they have not received any such message from Tehran.

The French news agency, AFP, quoted a source with the Supreme National Security Council in Tehran that "the message delivered today is not Iran's response to the six countries."

Iran had missed an ultimatum last weekend to respond to a "freeze-for-freeze" offer made by the five-plus-one – the five permanent members of the Security Council that includes United States, Britain, France, Russia and China, plus Germany, to freeze uranium enrichment in return for refraining from new U.N. sanctions.

The U.N. has already imposed three sets of sanctions against Iran over its nuclear program since 2006.

Washington, London and Paris on Monday threatened to seek tougher punitive measures at the United Nations if Tehran ignored their offer, which included launching talks on a long-term deal, recognizing Iran's right to develop nuclear energy for civilian purposes, and lifting sanctions – after an Iranian suspension.

Iranian commentators say that if Iran had sent a letter to Brussels, it was probably in response to revived Western threats and ultimatums, which Tehran has repeatedly resisted as preconditions to start "serious dialogue" about resolving its nuclear crisis with the West.

Iranian officials were quoted as saying that the purported letter to Solana, as well as Solana's telephone call with Iran's chief nuclear negotiator Saeed Jalili on Monday, did not touch on the five-plus-one deal or allude to uranium enrichment.

Tehran insists that its program is exclusively for energy purposes, saying its signature on the Non-Proliferation Treaty gives it the right to develop nuclear technology for peaceful purposes, but the West fears that it could be enriching uranium to eventually build nuclear weapons.

Iranian officials have warned they will not cooperate with the West under deadline threats, more sanctions or military threats [by the United States]; while commentators in Tehran say the more the threats, the greater the defiance.

Middle East analysts suggest there are no indications that the Islamic republic would accept the offer as it is for setting a precondition to halt enrichment before discussing a long-term arrangement; officials have given no sign that they are willing to submit to Western demands.

Analysts say that the U.S., British and French ultimatums giving Iran until the end of the day Tuesday to respond positively or face punitive measures seems to have added to Iranian defiance and/or stalling, suggesting that Tehran was probably drawing up a counterproposal that could prolong the negotiations with the European Union.

Iranian commentators complained that the ultimatum was a violation of an agreement reached with the European Union in a July 19 meeting that neither side would resort to deadlines, pressure or threats in order to maintain a positive diplomatic atmosphere for resolving the crisis.

The new ultimatum, it appears, gave Tehran a new justification for not giving the West the response it wants to the offer.

In any case, Iran seems indifferent to sanctions, which analysts agree have not worked in pushing the country to stop its nuclear centrifuge activities or making the Islamic republic any less determined to pursue its program.

An Arab diplomat told the Middle East Times that the best way to persuade Iran to make concessions on its activities is to accept its demands to pursue negotiations without first having to freeze its enrichment – in other words, do as the Iranians want.

Just as Iran, the world's fourth largest oil producer, demonstrated its political and economic strength by resisting Western pressure and ignoring sanctions, the Islamic republic again flexed its military muscles on Monday by announcing it had successfully test-fired an anti-ship missile with a 300-kilometer range that would allow it to threaten shipping through the busy Strait of Hormuz between Iran and Oman.

"No enemy vessels would be able to escape it," boasted the commander of the elite Revolutionary Guards, General Mohammad Ali Jaafari. "Given the equipment our armed forces have, an indefinite blockade of the Strait of Hormuz would be very easy."

Blocking the strait, a vital waterway through which much of the world's oil supplies passes, could disrupt the oil flow if tension is heightened – something that gives the Iranians an important edge in the nuclear bargaining with the West.

Meanwhile, a U.S. State Department spokesman said the six world powers will on Wednesday hold a conference call to decide on the next step in dealing with Iran if it does not respond to the latest incentives.