The United States said Thursday it "completely rejects" Iran's assertion that its nuclear program is for peaceful purposes only. Bush administration officials say they will press for a finding by the International Atomic Energy Agency, the IAEA, next month that Iran has violated the nuclear Non-Proliferation Treaty.

Officials here say concern is growing about the Iranian nuclear program, and that despite Tehran's assertions that the program is peaceful, there is no doubt among U.S. experts that Iran has mounted an aggressive, and until recently covert, drive to acquire nuclear arms.

The full extent of the Iranian weapons effort began to come to light last August. An Iranian opposition group published satellite photos of what it said were two weapons-related nuclear sites under construction in central Iran, one for enriching uranium and another for producing "heavy water," an essential ingredient for making plutonium.

Under international pressure, Iran allowed IAEA officials including Director-General Mohammed elBaradei to visit the sites in February. The New York Times reported Thursday that the visit revealed the presence of more than 100 uranium centrifuges, either completed or being assembled, at the enrichment site at Natanz.

The newspaper said the visit convinced U.S. and other nuclear experts that the Natanz site is so obviously weapons-related that the IAEA can be persuaded to take action on it when its governing board meets in Vienna June 16.

At a briefing here, State Department spokesman Richard Boucher answered in the affirmative when asked if the United States was pushing for an IAEA resolution against Iran, a move that could lead to U.N. sanctions against that country. He said Iran's intentions are clear despite its assertions that the suspect facilities are for power-generation:

"We've long made clear our concern, serious concern, about Iran's active pursuit of nuclear weapons as well as other weapons of mass destruction and longer-range missile delivery systems," he said. "Iran now openly admits that it is pursuing a complete nuclear fuel cycle. We completely reject Iran's claim that its is doing this for peaceful purposes."

Mr. Boucher said there is no economic justification for a oil-rich state like Iran to opt for nuclear power. He said while countries with peaceful nuclear programs have nothing to hide, Iran "did its best" to conceal its activities, while also refusing to sign protocols allowing greater scrutiny by the IAEA. He said U.S. concern about Iran is more acute because of its links to terrorism.

"Our concern is about the potential acquisition of nuclear weapons by a state that's a known supporter of terrorism. It's been something that the President talked about," he said. "It's why he talked about the "axis of evil." We all understand this to be one of the most dangerous combinations of our age. And the United States for many years has pressed very hard for people to end nuclear cooperation with Iran because we think that it contributes to that kind of development."

Earlier at a White House meeting with the Emir of Qatar, Sheikh Hamad Bin Kalifa al-Thani, President Bush said the United States has expressed its concerns about Iran both publicly and privately to other governments, including at his St. Petersburg talks with Russian President Vladimir Putin last November.

The United States has long sought to persuade Moscow to stop construction work at Iran's Bushehr nuclear power plant on the Persian Gulf. Though the reactor itself, due for completion next year, would be under international safeguards, U.S. officials contend it would give Iran vital know-how for its weapons program.