Iranian officials say they will not reverse course and halt their nuclear program. U.S. officials say they will keep pressure on Tehran to stop nuclear enrichment.
Iran's president says his country has the technology to produce nuclear fuel and will not turn back.
Iranian news agencies quote Mahmoud Ahmadinejad as comparing the program to a train that has left the station and is moving to its destination with no brake and no reverse gear.
When asked about the comments, U.S. Secretary of State Condoleezza Rice was blunt.
"They do not need a reverse gear. They need to stop."
The secretary of state told the ABC television program This Week that Iran knows what it has to do. She noted that there Iranians who are now questioning their government's defiance of a U.N. demand to halt uranium enrichment. Rice said Iranians are concerned that financial institutions are moving out of the country, and international investment is drying up.
"If you just read the press, you see the criticism of President Ahmadinejad by people inside Iran - knowledgeable and authoritative people in Iran - that the policies are isolating Iran."
The Iranian government says its nuclear program is purely civilian in nature, but the United States and its allies warn the same technology can be used to develop nuclear weapons. A U.N. deadline to cease nuclear enrichment came and went last week with no change in Tehran's position.
Officials from the Security Council plus Germany will meet Monday to discuss the next steps.
On ABC, and during an earlier appearance on the Fox News Sunday program, Rice emphasized her desire for a diplomatic solution. She told Fox News if Iran gives up its nuclear enrichment and reprocessing program, direct negotiations could result on the myriad of issues that divide Tehran and Washington.
"I have said that I am prepared to meet my counterpart or the Iranian counterpart at any time, if Iran will suspend its enrichment and reprocessing activities. That should be a clear signal."
One key Bush administration concern is Iranian influence on Shi'a Muslim militants in Iraq. The administration has presented evidence certain deadly weapons confiscated in Iraq had Iranian markings. They include the armor-piercing roadside bombs that have claimed the lives of more than 170 coalition troops in Iraq.
On CNN's Late Edition, Iraqi National Security Adviser Mowaffak al-Rubaie said there are signs of change.
"Recently, the Iranians have changed their position and we have some evidence they have stopped supplying arms or creating any of these mines in the streets of Baghdad."
Rubaie said there are also indications Iran has asked its allies in the Iraqi political arena to support the government of Nouri al-Maliki and give the Baghdad security plan a chance for success.