"Dialogue at this point may be interpreted as a sign of weakness," Livni told public radio.

"The United States under Obama's leadership is not ready to accept a nuclear Iran... There are, or we may have, some disagreements when dealing with the question of how to prevent it. I think that premature dialogue at a time where Iran thinks that the world has given up on sanctions may be problematic."

Israel has backed international diplomatic and economic sanctions against the Islamic republic but has never excluded a military strike to halt Iran's nuclear programme.

Obama warned during a visit to Israel earlier this year that a nuclear Iran would pose a "grave threat," but he nevertheless repeated his openness to meeting with its representatives, if the conditions were appropriate.

Israel considers Iran its main strategic threat because of Tehran's accelerating uranium enrichment programme, which Israel and the West believe is aimed at developing nuclear weapons.

Iran insists its nuclear programme is entirely peaceful.

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