The US has all options "on the table" including a military one to stop Iran from acquiring nuclear weapons, country's top Ambassador to the UN Susan Rice said today.

"United States President Barack Obama has been absolutely crystal clear that the US will not allow Iran to acquire a nuclear weapon and we will do what it takes to prevent that from happening. All options remain on the table. The president has been very clear about that and that includes the military option," Rice told the Fox News in an interview.

"This is not a policy of containment. As the president has repeatedly said, it's a policy to prevent Iran from acquiring a nuclear weapon. That is the bottom line or as the prime minister (Benjamin Netanyahu) prefers to call it, a red line. That's the bottom line," she said.

Noting that the Americans are in constant communication with Israeli security and intelligence and policy officials, Rice said that the US still thinks that there is scope through economic pressure which is unprecedented as well.

"Iran's economy is now shrinking by 1 per cent a year. Its oil production is down 40 per cent. Its currency has plummeted 40 per cent just in the last several months as sanctions have gone into fullest effect," she said.

"We think there is still time and space for that pressure to yield a result. The bottom line is the only way to permanently end Iran's nuclear programme is if it decides to give that programme up," she said.

"Now, the most solemn decision that a president can ever take is a decision to go to war. And President Obama's view is we will do what it takes it. But before we resort to the use of force, let us be sure we have exhausted other means including sanctions, pressure and diplomacy to ensure that Iran fully and finally gives up its nuclear weapons," Rice said.