New York - US President Barack Obama on Thursday said US-led sanctions had reduced Iran's economy to a "shambles," in a robust defence of his policy towards Tehran following sharp Republican attacks.
Obama had previously been reticent to respond to criticism by Republican candidates over his efforts to deter Iran's nuclear programme, but the president addressed the issue head on at a fundraising event in New York.
He said he had mobilised the world and built an "unprecedented" sanctions regime targeting Iran to state "unequivocally that we're not going to tolerate a nuclear weapon in the hands of this Iranian regime".
"We've been able to organise folks like China and Russia that previously would have never gone along with something like this," Obama said, referring to the support for sanctions of fellow UN Security Council permanent members.
"And it's been so effective that even the Iranians have had to acknowledge that their economy is in a shambles.
"When I came into office, Iran was united and the world was divided. And now what we have is a united international community that is saying to Iran, you've got to change your ways."
But Obama admitted that Iran had not yet decided to throw open its nuclear programme to international scrutiny in a way that would help it move out of isolation.
Republicans have savaged Obama's approach on Iran, saying it shows weakness and have even said that the president has failed to prepare for the possibility of a military attack against Tehran's nuclear programme.
"If we reelect Barack Obama, Iran will have a nuclear weapon. If you elect Mitt Romney... they will not have a nuclear weapon," the former Massachusetts governor and 2012 Republican frontrunner said in November.
Earlier this month Romney slammed Obama in South Carolina for being too slow to support the Iranian democracy protests in 2009.
"When there were over a million people in the streets of Tehran screaming for freedom, he was silent," Romney said.
Romney's rival Newt Gingrich has said the Iranian regime could be replaced within a year while Rick Santorum has compared Obama to "feckless" president Jimmy Carter, who saw hopes of a second term in 1980 dissolved in an Iranian hostage crisis.