Iran has refused to halt plans to build a nuclear reactor capable of producing atomic weapons in favor of a European-proposed alternative.
A foreign ministry spokesman (Hamid Reza Asefi) says Iran will not, under any circumstances, replace its heavy-water reactor.
Today's (Sunday's) announcement comes amid a series of talks between some European Union countries and Iran about Tehran's nuclear program.
EU officials have been trying to persuade Iran to give up its uranium enrichment program in exchange for economic incentives, and help in obtaining a light-water reactor, which can only be used for energy production.
The United States accuses Iran of secretly working to develop nuclear weapons. Tehran strongly denies the allegation, insisting its nuclear program is only for making electricity. A published report says the United States has been flying drones over Iran for almost a year to look for evidence of nuclear weapons programs and detect weaknesses in air defenses.
The Washington Post reports today (Sunday) the U.S. military has been launching the unmanned aircraft from bases in Iraq. The newspaper says that according to three U.S. officials with detailed knowledge of the secret effort, the drones use radar, video, still photography and air filters designed to pick up traces of nuclear activity.
The aircraft were first spotted in December by Iranian civilians.
Iran is said to have filed an official protest through Swiss channels, as Washington and Tehran do not have diplomatic relations.