President Bush says the world will not tolerate nuclear weapons in Iran. He is also calling on Iranian leaders to treat anti-government protesters with respect.
Iran denies it is developing nuclear weapons. But the Bush administration says it has grave concerns about Tehran's nuclear intentions.
President Bush points out it is a topic he has discussed at length with other world leaders.
"The international community must come together to make it very clear to Iran that we will not tolerate construction of a nuclear weapon," he said. "Iran will be dangerous if they have a nuclear weapon."
The comments came as the U.N.'s nuclear watchdog agency debated a new report that claims Iran has refused to declare the import, processing and storage of nuclear materials despite promises to do so.
The debate is taking place at the Vienna, Austria headquarters of the International Atomic Energy Agency, and has been marked by sharp words between U.S. and Iranian officials.
On Wednesday, the U.S. representative to the IAEA accused Tehran of violating non-proliferation agreements and stalling on nuclear inspections. Iran's representative denied the accusations, raising questions about the impartiality of the agency report on its nuclear program.
White House Spokesman Ari Fleischer said there was no pressure exerted by the United States, and scoffed at the notion Washington could dictate the work of any U.N. agency.
"I think as you noted from recent events involving the United Nations and the IAEA, these are proudly independent organizations that call it as they see it and make their own judgments," he said.
Another issue creating friction between the Bush administration and Tehran is the fate of Iranian anti-government protesters. Iran has accused the United States of interfering in its internal affairs. President Bush makes clear the demonstrators have his moral support.
"I appreciate those courageous souls who speak out for freedom in Iran," he said. "They need to know American stands squarely at their side. And I would urge the Iranian administration to treat them with the utmost respect."
The demonstrations began last week and resulted in clashes between the demonstrators and government supporters. The protests have died down over the last few days.