Iran has told the United Nations nuclear agency it is considering a proposed deal on its nuclear programme in a favourable light but needs until the middle of next week to respond.
The International Atomic Energy Agency (IAEA) had set a deadline of Friday for responses to the draft deal which has been agreed to by the US, France and Russia.
In a statement, IAEA chief Mohamed ElBaradei said he hoped Iran's response "will equally be positive, since approval of this agreement will signal a new era of co-operation".
Earlier, Iranian state television reported that Iran would prefer to buy uranium for its research reactor, rather than send its own stock abroad for enrichment as proposed, the BBC reports.
The deal requires Iran to send 1.2 tonnes of its known 1.5-tonne stockpile of low-enriched uranium to Russia and France by the end of the year, where it would be processed and returned, the Reuters news agency reported.
The enriched uranium would be difficult to use for warheads but able to be used for its research reactor and for medical use.
The plan is seen as crucial to start defusing a standoff between Iran and world powers over its contested nuclear ambitions.
Western powers fear Iran's nuclear programme is aimed at producing weapons while Iran insists it is solely for peaceful purposes.
A US State Department spokesman said the US hopes Iran will respond positively.