For the first time in more than a year, the Obama administration will return to nuclear negotiations with Iran.

Iran will meet with six world powers at a gathering in Istanbul, Turkey, on Saturday. U.S. leaders are hoping to make enough progress to hold off Israel's urgent calls for action.

A nuclear Iran may be the greatest threat to the Jewish state's existence. Israeli military officials believe they may need to strike Iran's nuclear facilities by the summer to effectively prevent an attack.

U.S. officials admit the window for a diplomatic breakthrough is closing. If the weekend's talks fail completely, all U.S. options remain on the table.

Secretary of State Hillary Clinton has called on Iran to prove its uranium enrichment activity is for peaceful purposes.