Rice told Fox News Sunday that Iran remains a "dangerous state" that was trying to develop the capacity to use nuclear power for military purposes and even make nuclear weapons.
"The Iranians every day demonstrate why the United States has been so hard on them and why the president put Iran into the axis of evil when he talked about Iraq, North Korea and Iran in 2002," she said.
The national security aide said Washington was working with its European allies and the International Atomic Energy Agency (IAEA) to persuade Tehran to drop its nuclear weapons ambitions or face isolation.
The United States was also putting pressure on Russia to curb transfers of nuclear technology to Iran, she said, adding "we've been very clear that these rogue states that seek weapons of mass destruction are a danger."
"It's a very tough situation. But we believe that this is one that still has a diplomatic solution within sight," Rice said, speaking from Turkey ahead of a NATO summit. She did not elaborate.
The IAEA, the UN nuclear watchdog, rebuked Iran on June 18 for failing to come clean about its nuclear program but the Islamic Republic has shown little inclination for conciliation.
Tehran said Sunday it would resume construction of centrifuges for uranium enrichment while continuing to suspend enrichment itself. But a senior member of parliament said the assembly would push to resume the process.
Rice's remarks appeared part of a general US move to step up the rhetoric against Iran, which President George W. Bush famously lumped with Iraq and North Korea in an "axis of evil" in his State of the Union speech two years ago.
Earlier Sunday, Defense Secretary Donald Rumsfeld delivered his own broadside at the Iranian government, accusing it of "not telling the truth about its role in nuclear development."
"Most recently, we have seen them resisting the UN processes that they have previously seemed to have agreed to, but obviously are not adhering to," Rumsfeld said in an interview with the BBC.