Iran will not give its final answer at a meeting this week to a package of proposals backed by six world powers that aims to end a nuclear standoff with the West, an Iranian nuclear official said on Sunday.

An oil rig in China's Bohai Sea is seen in a file photo. Oil edged below $74 a barrel on Monday, extending the previous session's 1.4 percent fall on expectations of progress in talks on Iran's nuclear program. [Reuters]

Iranian chief nuclear negotiator Ali Larijani meets European Union foreign policy chief Javier Solana on Tuesday, when the EU has said it wants a "substantial response" to the offer.

Iran previously said it would not give a final response on Tuesday but, by repeating the comment a day before the meeting, the official undermined any prospects of a breakthrough.

"Tomorrow, we will not give a definite answer. We will only discuss questions and ambiguities regarding the offer," the official said.

Asked if Iran would give a final response if Solana answered all the queries, the official said: "It is very unlikely."

The United States, Russia, China, France, Britain and Germany offered Iran a package of economic and diplomatic incentives to give up uranium enrichment, a process the West says Iran is using to make atomic bombs despite Iranian denials.

Iran, which says the package contains ambiguities that need clearing up, has said it would give an answer by August 22. Iranian Foreign Minister Manouchehr Mottaki said on Sunday that Solana was not able to answer all Iran's questions.

Mottaki also said the Group of Eight countries, which meet in Russia in mid-July, should not take decisions that could harm the current positive atmosphere in efforts to resolve the issue.

The nuclear package is expect to be one of the issues dominating the G8 meeting.