Iran's supreme leader Ayatollah Ali Khamenei said he saw "no use" in negotiating with the United States over its nuclear program and signalled again that Tehran was unwilling to freeze sensitive uranium enrichment work.

Iranian President Mahmoud Ahmadinejad (C) attends a departure ceremony in Tehran June 27, 2006. [Reuters]

Although Khamenei said Iran was ready to ease international concerns over its disputed atomic drive, he said "negotiations with the United States are of no use for us. We have no need for such negotiations."

"We will not negotiate with anyone over the undeniable right of nuclear technology and using it," he added, indicating Tehran will refuse to bow to international demands to suspend uranium enrichment.

The US administration said it did not view the comments as Iran's final word on the issue and would wait for a formal response to an offer from Washington and other world powers.

On June 6, EU foreign policy chief Javier Solana presented Iran with an offer -backed by Britain, China, France, Germany, Russia and the United States - of multilateral talks and a variety of incentives.

The offer - which would pave the way for the first substantive contacts between Iran and the United States in decades -- is conditional on Iran first agreeing to suspend enrichment work, the focus of suspicions that the Islamic regime wishes to acquire nuclear weapons.

But Iran appears to still reject the key condition and continues to call for negotiations without any "preconditions".

"If they recognise this right, we are ready to negotiate over supervision controls," Khamenei said of Iran's nuclear programme, which the regime insists is merely aimed at generating electricity.

In Washington, the White House played down Khamenei's comments and said Iran's position remained unclear.

Asked whether Iranian leaders were signalling that they would ignore a US call for a formal response to the proposal in "weeks, not months," Snow replied: "Well, no they're not."

"Keep in mind that there are differences between public and private statements," he told reporters, adding that "there have been conversations" between Iran and Britain, France and Germany, "and we expect the Iranians to provide a proper answer within the span of weeks and not months."

Later, pressed on whether he had meant to signal that Iran's private responses were more positive than its public statements, Snow replied: "I make absolutely no attempt to characterize - good, bad, or indifferent."

Snow said the United States would only recognise a formal answer given by Iran's senior nuclear negotiator, Ali Larijani, to European Union foreign policy chief Javier Solana.

"The position has always been the same, which is: When Mr Larijani communicates with Javier Solana, that is how we expect to have an answer to the proposal," Snow told reporters.

Diplomats said hopes had dimmed that the two would meet this week despite an informal deadline on Thursday for Iran to declare to world powers if it would suspend uranium enrichment.

Iranian President Mahmoud Ahmadinejad has said a reply to the proposal will be given in late August. In contrast, the major powers are calling for a reply before the end of June in time for a summit of the G8 group of industrialised nations in Russia.

UN Secretary General Kofi Annan on Tuesday also urged Iran to expedite its response to the offer of incentives.

Annan conveyed his view "that Iran should speed up its response to the proposals" in a meeting with Iranian Foreign Minister Manouchehr Mottaki at UN headquarters in New York, a UN statement said.

But President Vladimir Putin said, in a thinly veiled reference to US-led pressure on Iran, that Russia will not join any ultimatums over the problem of nuclear proliferation.

"We do not intend to join any sort of ultimatum, which only pushes the situation into a dead end, striking a blow against the authority of the UN Security Council," Putin told Russian diplomats in Moscow in the presence of journalists.

Russia, a key economic ally of Iran, has consistently resisted Western pressure in the current international impasse over US and European claims that Tehran is using a Russia-backed civilian nuclear programme to mask a secret bomb-making project.

The United States has not ruled out seeking UN sanctions or even military action should Iran refuse the talks.