"We're… going through the UN this month to present sanctions," President Barack Obama's national security advisor, retired general James Jones, told Fox News Sunday.
While the US is not actively seeking to destabilize Iran, which has been rocked by months of anti-government protests since disputed elections last year, Jones said additional sanctions could nevertheless have that effect.
"We know that internally there is a very serious problem. We're about to add to that regime's difficulties by engineering, participating in very tough sanctions, which we support," he said.
"Not mild sanctions. These are very tough sanctions. A combination of those things could well trigger a regime change — it's possible."
Jones said that "the combination of internal and external problems are certainly not going to make life easier for the government of Iran."
His remarks cane with Secretary of State Hillary Clinton in the Middle East to build the US case for tougher sanctions over Iran's suspect nuclear activities in meetings with key Arab and Muslim leaders.
Jones said there was already "tremendous support" for new sanctions against Iran, but admitted: "We need to work on China a little bit more.
"Russia is supportive and is on board, and has been a steady friend and ally on this with president Obama," he said, warning: "I think Iran needs to weigh very carefully how it wishes to proceed."
With Russia having hardened its stance, China is the sole veto-wielding hold-out to further sanctions at the UN Security Council and is still pushing for further negotiations
However US Vice President Joe Biden expressed confidence Sunday that the Chinese would ultimately join the other nations in backing measures to punish Iran.
"I believe we'll get the support of China to continue to impose sanctions on Iran to isolate them, to make it clear that in fact they cannot move forward," he told NBC's "Meet the Press" program.
There is strong backing for sanctions from Britain and France — the remaining veto-wielding members — as well as from Germany, which has also been involved in months of negotiations to try and get Iran to change tack.
The West is trying to convince Tehran to sign on to an UN-brokered deal that calls for it to ship its stockpile of low-enriched uranium (LEU) abroad for further processing.
So far, Iran has defied three sets of UN Security Council sanctions, insisting its nuclear drive is peaceful.
This week it boasted that it had begun enriching its uranium stockpile to the 20 percent level that would allow it to fuel its research reactor.
Western powers believe Iran's eventual goal is to make the highly enriched uranium that would allow it to build a nuclear weapon and radically alter the balance of power in the already unstable Middle East and Central Asia.
But analysts warn that President Mahmoud Ahmadinejad may be exaggerating Iran's ability to advance its nuclear program in order to force the West to negotiate on his terms and reinforce his shaky position at home.
Biden supported that view, asserting Sunday that Iran "is not a nuclear power."
"The progress that Iran has made on the nuclear front is greatly exaggerated in my view," Biden told NBC, saying that Iran made the announcement to draw attention away from ant-government protests and other domestic problems.
"I can understand why Ahmadinejad would make that assertion, to divert the world's attention from the abuse of the civil liberties and civil rights of the people of Iran," Biden said.
Thirty-one years after the Islamic revolution, Tehran's authoritarian regime is facing unprecedented street protests from a large but diffuse opposition movement, which some think could topple the government.
