"Iran will never give in to the illegitimate and illegal pressure of the West (to freeze its uranium enrichment)," said Ali Asghar Soltanieh in a speech in London about the nuclear Non-Proliferation Treaty.
The EU's top diplomat, Javier Solana, presented Tehran on Saturday with a new package of economic incentives designed to persuade it to curb its nuclear work, which the West fears is aimed a building a nuclear weapon.
Solana said Iran should stop enrichment during negotiations to implement the offer.
The package agreed by the United States, Russia, China, Britain, France and Germany last month and delivered by Solana is a revised version of one rejected by Iran in 2006.
The U.N. Security Council has hit Iran with three rounds of sanctions for refusing to halt its enrichment work, as demanded by the council.
Western powers have warned Iran it would face more sanctions if it spurns the offer. So far Iran has shown no sign it will change its position, and suggested it was in no hurry to respond to the latest offer.
A senior Iranian official, who asked not to be named, told Reuters on Tuesday Iran's answer would not be a straight yes-or-no answer, adding that it would be a "discussable response".
As a signatory to the Non-Proliferation Treaty, Iran insists it has the right to master the complete nuclear fuel cycle, including enriching uranium, for peaceful purposes.
Tehran says it wants only electricity from enriched uranium, a process that provides fuel for power plants or, if concentrated to heighten the enrichment level, atomic bombs.
British Prime Minister Gordon Brown said on Monday that Europe would take further sanctions against Iran, speaking of immediate action to freeze the overseas assets of Iran's biggest bank, the Bank Melli.
However, after a meeting of EU foreign ministers on Monday, Solana said the block had yet to take a decision to launch a new round of sanctions against Iran over its nuclear program.
