Western powers gave Iran two weeks from July 19 to respond to their offer to hold off on imposing more U.N. sanctions on Iran if Tehran would freeze any expansion of its nuclear work.
That would suggest a deadline of Saturday, although Russia, one of the six powers facing Iran, has opposed a deadline and Iran dismissed the idea of having two-weeks to reply.
Iran's President Mahmoud Ahmadinejad said the nuclear issue was just an excuse for the country's foes.
"The main reason for their enmity with this nation in the past 30 years is that they want to force the Iranian nation to retreat," the state broadcaster quoted him as saying, without mentioning any country by name.
"Whenever the enemies have failed against this nation they have tried to make excuses, but the Iranian nation will stand against them with its power," Ahmadinejad said, without elaborating.
Ahmadinejad's remarks drew a speedy reaction from the White House.
"Comments like those aren't productive. He should instead be focused on the generous incentives package we've offered," White House spokeswoman Dana Perino said in Kennebunkport, Maine.
The West accuses Iran of seeking to build nuclear warheads under cover of a civilian power programme. Iran, the world's fourth largest oil producer, denies the charge.
The freeze idea is aimed at getting preliminary talks started, although formal negotiations on an incentives package proposed by six world powers will not start before Iran suspends uranium enrichment, which has both civilian and military uses.
Iran has rejected suspension in the past and has given no indication so far that it is ready for a freeze.
(Reporting by Zahra Hosseinian; Writing by Fredrik Dahl; Editing by Richard Balmforth)
