US Secretary of State Hillary Clinton said Monday the United States will not "compromise its commitment" to prevent Iran getting a nuclear bomb, but sanctions that bite will take time.

In excerpts of a speech she will deliver to the pro-Israel lobby AIPAC, Clinton said it "is taking time to produce these sanctions... but we will not compromise our commitment to preventing Iran from acquiring these weapons."

Clinton said that elements in Iran's government have become a menace, both to their own people and in the region, saying that Iranian President Mahmoud Ahmadinejad fomented anti-Semitism and threatened to destroy Israel.

"In addition to threatening Israel, a nuclear-armed Iran would embolden its terrorist clientele and would spark an arms race that could destabilize the region," the secretary of state said.

"This is unacceptable. Unacceptable to the United States. Unacceptable to Israel. And unacceptable to the region and the international community."

She added that the United States was determined to prevent Iran from acquiring nuclear weapons.

"We are working with our partners in the United Nations on new Security Council sanctions that will show Iran's leaders that there are real consequences for their intransigence, that the only choice is to live up to their international obligations," Clinton said. "Our aim is not incremental sanctions, but sanctions that will bite."

She noted that it was taking time to produce these sanctions, but added that the US administration believed that time was a worthwhile investment for winning the broadest possible support for its efforts.

"But we will not compromise our commitment to preventing Iran from acquiring these weapons," the secretary of state said.

The West accuses Iran of developing nuclear technology to produce atomic weapons, a charge Tehran denies.

Israel is widely reported to be the only nuclear-armed power in the Middle East, but it refuses to confirm or deny this, instead pursuing a policy of "nuclear ambiguity."

On Saturday, US President Barack Obama subtly shifted US rhetoric on Iran, pledging to ensure Iranians could access the Internet without fear of censorship, and blaming Tehran for isolating itself.

A year after offering a "new beginning" to Iran, Obama used his annual Nowruz New Year's message to keep the door to dialogue open, but reached out more to the Iranian populace rather than to their leaders in Tehran.

"Even as we continue to have differences with the Iranian government, we will sustain our commitment to a more hopeful future for the Iranian people," Obama said in his message released by the White House.

The president repeated the now familiar line that Iran had failed to live up to its obligations to come clean on its nuclear program, so should be held accountable by world powers now seeking a tougher sanctions regime.