The US national security adviser has called for Iran to respond as early as next week to a UN package of incentives on its nuclear programme.
Tehran says it is entitled to enrich uranium for peaceful purposes
Stephen Hadley said it would be "helpful" to have a response before a cycle of G8 meetings began on 29 June.
On Wednesday Iran's president said a reply would come on 22 August.
The UN package reportedly offers help with a civil nuclear programme but demands Iran suspend uranium enrichment as a precondition to negotiations.
UN Secretary-General Kofi Annan has said Iran is considering the offer "very, very seriously", after talks with the Iranian foreign minister in Geneva.
But Mr Annan said it was unlikely that any response to the offer would come before mid-July.
The package of measures is backed by the five permanent members of the UN Security Council, plus Germany, and was delivered to Tehran on 6 June.
President George Bush has said he wants a reply in "weeks, not months", and on Wednesday he said 22 August seemed "an awfully long time for a reasonable proposal".
On Thursday, Mr Hadley added his voice, urging Iran to respond before a series of G8 meetings. Foreign ministers from the group of eight industrialised nations are meeting in Moscow on 29 June, followed by a summit of G8 leaders in St Petersburg on 15-17 July.
"It would be helpful and useful if we could get a response and know where the Iranians are before those meetings," Mr Hadley told reporters in Budapest.
"It would advance the negotiating process," he said.
The package is said to offer help with Iran's civilian nuclear programme and to guarantee supplies of reactor fuel, as well as various trade advantages and security guarantees.
It requires Iran to halt its production of enriched uranium, which can also be used in nuclear warheads.
The US believes Iran is trying to make nuclear weapons but Tehran says it is enriching uranium for energy purposes, as it is entitled to under the terms of the nuclear Non-Proliferation Treaty, to which it is a signatory.
In his speech on Wednesday, Iranian President Mahmoud Ahmadinejad again stressed Iran had "definite and legitimate rights" to a nuclear programme.
"We will negotiate with everyone... but negotiations should be as equals and without any preconditions imposed," he said.
EU foreign policy chief Javier Solana, who delivered the package of proposals to Iran on 6 June, says he expects to meet the Iranian top nuclear negotiator Ali Larijani in the next week, according to Reuters news agency.
He is offering to clarify what Mr Larijani has called "ambiguities" in the proposal.