"I can confirm High Representative Ashton received the letter from Dr. [Saeed] Jalili today," Maja Kocijancic, a spokeswoman for Ashton, told Yahoo News Wednesday. "We are carefully studying the letter and consulting with our E3+3 partners" on their response.

The long-awaited Iranian RSVP comes as the Obama administration said this week that it believes Iran wants to return to nuclear negotiations, Yahoo News reported Tuesday. Dennis Ross, Obama's former adviser on Iran, repeated the claim in an op-ed in the New York Times on Wednesday.

Analysts are cautious about what could be achieved in any talks. The last time Iran formally met with world powers --in January 2011 in Istanbul--the meeting was so unproductive, western diplomats resolved afterwards to suspend the negotiating track until Iran agreed to serious negotiations.