Washington: President Barack Obama on Friday defended his policy on Iran amid criticism from the Republican party, saying Tehran is more isolated than ever.

Obama said Iran is more isolated than ever and international community is more unified than ever in imposing toughest sanctions on it.

Obama said at a White House news conference that his administration "has systematically imposed the toughest sanctions on Iran ever".

He said when he came into office, the world was divided and Iran was unified and moving aggressively on its own agenda.

"Today Iran is isolated, and the world is unified and applying the toughest sanctions that Iran's ever experienced, and it's having an impact inside of Iran," Obama said.

He said it was a consequence of the extraordinary work done by his national security team.

He said Iran understands that they have a choice either to "break that isolation by acting responsibly and forswearing the development of nuclear weapons", or "can continue to operate in a fashion that isolates them from the entire world".

"If they are pursuing nuclear weapons, then I have said very clearly that is contrary to the national security interests of the United States. It's contrary to the national security interests of our allies, including Israel. We are going to work with the world community to prevent that,” Obama said.

Ahead of the November 2012 presidential elections, several Republican White House candidates have portrayed Obama as unable or unwilling to take tough policy on Iran.