"The crucial moment is not the day of the bomb. The crucial moment is the day in which Iran will master the enrichment, the knowledge of enrichment," she said on CNN's "Late Edition."

Livni, whose country is the only Middle East power possessing nuclear weapons, said she did not want to identify a point of "no return" in the controversy over Iran's nuclear program.

The Iranians, she said, "are trying to send a message that it's too late, you can stop your attempts because it's too late. It's not too late. They have a few more months," she said.

"The world cannot afford a nuclear Iran," Livni said. "I believe that this is time for sanctions."

Iran, whose president last year called for Israel to be "wiped off the map," denies it is seeking nuclear weapons.

Livni said Israel would like to help strengthen the more moderate elements within the Palestinian Authority -- such as President Mahmoud Abbas -- at the expense of the militant Hamas movement, which swept to power after winning January elections.

Livni called on the international community to unite to make Hamas take certain steps as a prelude to talks. She did not specify the steps, but did mention Israel's demand that Hamas release an Israeli soldier captured in June.

"If the international community show determination in the next few weeks, maybe this is the moment in which Abu Mazen can be strengthened and Hamas will have to do something," she said, referring Abbas.

Abbas and Hamas, which seeks Israel's destruction, accused each other on Sunday of trying to derail a planned unity government that Palestinian officials hope will lift Western sanctions imposed after Hamas' election victory.

Abbas and Livni will both be in New York to attend the U.N. General Assembly in the coming week.