JERUSALEM — The U.S. and Britain on Sunday urged Israel not to attack Iran’s nuclear program as the White House’s national security adviser arrived in the region, reflecting growing international jitters that the Israelis are poised to strike.

Israel knows time is short, and that they have to do something very soon...

In their warnings, both the U.S. joint chiefs of staff, Gen. Martin Dempsey, and British Foreign Minister William Hague said an Israeli attack on Iran would have grave consequences for the entire region and urged Israel to give international sanctions against Iran more time to work. Dempsey said an Israeli attack is “not prudent,” and Hague said it would not be “a wise thing.”

Both Israel and the West believe Iran is trying to develop a nuclear bomb — a charge Tehran denies. But differences have emerged in how to respond to the perceived threat.

The U.S. and the European Union have both imposed harsh new sanctions targeting Iran’s oil sector, the lifeline of the Iranian economy. With the sanctions just beginning to bite, they have expressed optimism that Iran can be persuaded to curb its nuclear ambitions.

On Sunday, Iran’s Oil Ministry said it has halted oil shipments to Britain and France in an apparent pre-emptive blow against the European Union. The semiofficial Mehr news agency said the National Iranian Oil Company has sent letters to some European refineries with an ultimatum to either sign long-term contracts of two to five years or be cut off. The 27-nation EU accounts for about 18 percent of Iran’s oil exports.

Israel has welcomed the sanctions. But it has pointedly refused to rule out military action and in recent weeks sent signals that its patience is running thin.

Israel believes a nuclear-armed Iran would be a threat to its very existence, citing Iran’s support for Arab militant groups, its sophisticated arsenal of missiles capable of reaching Israel and its leaders’ calls for the destruction of the Jewish state.

Last week, Israel accused Iran of being behind a string of attempted attacks on Israeli diplomats in India, Georgia and Thailand.

There is precedent for Israeli action. In 1981, the Israeli air force destroyed an unfinished Iraqi nuclear reactor. And in 2007, Israeli warplanes are believed to have destroyed a target that foreign experts think was an unfinished nuclear reactor in Syria. source – MSNBC