European Union foreign policy chief Javier Solana will hold new talks with Iran's top nuclear negotiator Ali Larijani, as well as representatives from Britain, France, Germany and Russia.

"It's clear that we need the response (of the Iranians) as soon as possible, and that the time element is very important," said Solana's spokeswoman Cristina Gallach.

"We have to exert pressure so that this happens as soon as possible," she insisted on the eve of the talks, which come after a private dinner between the two men in Brussels last Thursday.

The international offer, presented to Tehran by Solana on June 6 on behalf of the five permanent UN Security Council members plus Germany, offers economic and other incentives in exchange for a pledge to suspend uranium enrichment.

The West, in particular the United States, wants Tehran to respond before a Group of Eight (G8) summit in Saint Petersburg next week, but hardline President Mahmud Ahmadinejad has said Tehran will not respond before August.

Iran has played down prospects of substantial progress, saying it sees the meeting is a chance to "resolve ambiguities" about details of the offer, underlining that it will not give a full response in Brussels.

On Sunday it again dashed hopes of a rapid response to the offer by saying it will take until the second half of August to respond.

"They need to respond to the ambiguities we have identified," Foreign Minister Manouchehr Mottaki said in Tehran. "We will respond in the last week of Mordad," Mottaki added, referring to the Iranian month which ends August 22.

But the US administration has made it clear that it wants a substantial response from Tehran before the G8 summit.

"The G8 will be an opportunity for those of us involved with this issue to make it clear to the Iranians that we're firm in our resolve for them not to have a nuclear weapon," US President George W. Bush said Friday.

The West has made it clear that a rejection of the offer by Tehran would relaunch debate at the UN Security Council over what further measures to take against Iran.

But it is unclear exactly where this would lead, in particular since Russia and China, which have veto rights, have made it clear they oppose sanctions against Tehran.

The US State Department's number three said Sunday that Tehran has "miscalculated" by trying to drive a wedge between the United States and its allies.

"They thought they could divide the United States from our European allies and Russia and China, but we've been able to craft a united coalition of all those countries," Nicholas Burns told NBC television.

"They have to choose -- negotiations with us, or further action in the Security Council," Burns said.

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