US President Barack Obama on Thursday said US-led sanctions had reduced Iran's economy to a "shambles," in a robust defense of his policy towards Tehran following sharp Republican attacks.
Obama had previously been reticent in responding to Republican campaign attacks over his efforts to deter Iran's nuclear program, but addressed the issue at a Jewish community fundraising event in New York.
He said he had mobilized 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 organize 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 program to international scrutiny in a way that would help it move out of isolation.
Obama spoke hours after European Union nations agreed to sanction Iran's central bank, freezing assets used to finance its nuclear drive, in a move that further penalized and isolated the Islamic state.
The US leader signed into law a new set of US sanctions last month which target Iran's oil sector and seek to make foreign firms choose between doing business with Tehran or the United States.
Republicans seeking to turf Obama out of office in November's election have savaged his approach on Iran, saying that 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 program.
"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, in South Carolina, Romney slammed Obama 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.
Obama also told the mainly Jewish audience in New York that he had not seen the progress he had hoped for in his efforts to forge peace between Israel and the Palestinians.
And he also implicitly took aim at another area of Republican criticism that he had weakened US support for Israel.
"We've got the strongest military cooperation that we've ever had between our two nations. That's not my opinion, by the way -- that's the Israeli government's opinion," he said.