"Iran, Hamas and other extremists are testing our attitude, and they must understand that the world will not be tolerant towards extremists and terrorism," she said.

"It is of the utmost importance that we keep up our coordination against the Iranian threat because time is not on the side of the moderates," she was quoted as saying in the call initiated by Biden, according to the ministry.

Israel's Defence Minister Ehud Barak on Friday issued a thinly veiled call for the United States not to rule out the possibility of a military strike against Iran because of its nuclear ambitions.

"We don't rule out any option. We recommend others don't rule out any option either," Barak told journalists after talks with visiting US Secretary of State Condoleezza Rice.

Tehran denies it wants nuclear weapons, and says its atomic project is purely peaceful.

The previous day, Livni herself said that possible US talks with Iran may be problematic, highlighting possible disagreements with a Barack Obama administration.

"Dialogue at this point may be interpreted as a sign of weakness," she said.

President-elect Obama warned during a visit to Israel in July that a nuclear Iran would pose a "grave threat," but he also reiterated his openness to meeting Tehran's representatives if the conditions were right.

Israel itself is widely considered to be the only nuclear-armed state in the Middle East, although it has never officially confirmed nor denied having such weapons.

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