Mohamed ElBaradei said “the earlier they can provide an answer” on the UN offer to get Tehran to halt uranium enrichment “is better for everybody.”
His comments came before Iran’s top nuclear negotiator arrived in Brussels ahead of rescheduled talks with the EU.
Ali Larijani said his country was serious about continuing negotiations.
In Washington, a state department spokesman told reporters “it’s high time that they provide an answer”.
Sean McCormack said foreign ministers of the US, Russia, China, Britain, France, Germany and the EU would meet next Wednesday to discuss negative steps against Iran if it had not given a clear answer, Reuters news agency reported.
‘Playing for time’
Mr Larijani is meeting EU Foreign policy chief Javier Solana for an informal dinner in Brussels, while formal discussions have been scheduled for next week.
Iran postponed a meeting scheduled for Wednesday, citing security concerns.
Correspondents say the announcement appeared to be linked to a visit to the European parliament by the leader of a controversial exiled Iranian opposition group.
The BBC’s Pam O’Toole say the postponement has stoked suspicions in some Western countries that Iran, under threat of UN Security Council action if it rejects the package, is playing for time.
Thursday’s dinner is the first face to face meeting between Mr Larijani and Mr Solana since early June, when Mr Solana presented Iran with the package of proposals.
In public statements, Iranian officials have reacted relatively positively to the package, but have also said there are ambiguities which need to be ironed out.
Time pressure
But Tehran has yet to give an official substantive response, despite pressure from Western countries for it to do so before the G8 summit in St Petersburg in mid-July.
Various Iranian officials have suggested that Tehran might give a formal response in early – or even late – August.
There seems to be little expectation that Mr Larijani will definitively accept or reject the proposals during Thursday’s meeting.
But the EU says it is hoping to get at least an initial indication of what Iran is thinking – and to answer any questions it has on the package, in the hope of obtaining a substantive response next week.
