Stopping short of calling it a diplomatic breakthrough, top US and EU officials expressed cautious optimism over prospects that Iran may be willing to engage major powers in new talks, but emphasised that any dialogue should be focused on the nuclear issue.
"It's good to see that the letter has arrived and that there is a potential possibility that Iran may be ready to start talks," European foreign policy Catherine Ashton told reporters at a joint media availability with Secretary of State Hillary Clinton.
Ashton said she received a letter from Iran in response to her letter in October last year. "We are consulting colleagues and analysing closely what this letter would mean."
Clinton said international community has been looking to Iran to demonstrate it is prepared to come to the table in a serious and constructive way.
The new hope of negotiations comes after weeks of bluster including ominous threats of military action in the Persian Gulf and terror strikes on Israeli diplomats in India, Thailand and Georgia that Tel Aviv has blamed on Iran.
Clinton said: "We have been reviewing Iran's proposal to resume talks on its nuclear activities and consulting closely between us and with our other P-5 plus one partners. This response from the Iranian government is one we've been waiting for, and if we do proceed, it will have to be a sustained effort that can produce results."