Iran's president, Mahmoud Ahmadinejad, has called the U.S. decision to send a representative to international nuclear talks in Geneva a "positive step."
But he reiterated Wednesday that his country will not back down in the face of international pressure to suspend sensitive nuclear activities.
Mr. Ahmadinejad vowed Iran will continue to pursue nuclear technology despite the efforts of what he called oppressive powers.
In Washington, White House spokeswoman Dana Perino said Mr. Ahmadinejad's statements continue to isolate the Iranian people from the international community.
Earlier this week, U.S. Secretary of State Condoleezza Rice said Iran could face additional sanctions if it does not suspend uranium enrichment.
Rice said Iran failed to give a serious response to a package of incentives during nuclear talks with world powers in Geneva Saturday.
She warned that world powers are in the strongest possible position to return to sanctions if Iran does not act.
The United States and its Western allies have accused Iran of working to produce a nuclear weapon. Iran says its nuclear program is peaceful.
Iranian and European Union negotiators have agreed to meet again in two weeks.
Highly enriched uranium can be used to build a nuclear weapon.Some information for this report was provided by AFP and AP.