TEL AVIV, Israel -- U.S. and Israeli defense officials welcomed a new arms sale agreement Monday as a major step toward increasing Israel's military strength, but Israeli officials said it still left them without the weapons they would need if they decided to attack Iran's deepest and best-protected nuclear sites.
The mixed message came as Defense Secretary Chuck Hagel and his Israeli counterpart, Moshe Yaalon, reaffirmed their commitment to stopping Iran from obtaining nuclear arms, while sidestepping continuing discord between the two countries about how close to allow Iran to get toward such a goal.
In public, Mr. Hagel again said Israel had the right to decide by itself how to defend the country, and both officials said military action should be a last resort. But a close adviser to Prime Minister Benjamin Netanyahu said Monday that "the fundamental difference of views on how much risk we can take with Iran is re-emerging."
The new weapons sale package includes aircraft for midair refueling and missiles that can cripple an adversary's air defense system. Both would be critical for Israel if it were to decide on a unilateral attack on Iran.
But what the Israelis wanted most was a weapons system that is missing from the package: a giant bunker-busting bomb designed to penetrate earth and reinforced concrete to destroy deeply buried sites. According to both U.S. and Israeli analysts, it is the only weapon that would have a chance of destroying the Iranian nuclear fuel enrichment center at Fordow, which is buried more than 200 feet under a mountain outside the holy city of Qum.
The weapon, called a Massive Ordnance Penetrator, weighs about 30,000 pounds -- so much that Israel does not have any aircraft capable of carrying it. To do so, Israel would need a B-2 bomber, the stealth aircraft that the United States flew nonstop recently from Missouri to the Korean Peninsula to underscore to North Korea that it could reach their nuclear sites. The Obama administration has been reluctant to even discuss selling such capability to the Israelis.
Iran has consistently denied that it wants nuclear weapons and has called its uranium enrichment activities peaceful.
The Fordow site has become an increasing source of concern to the Israelis. When they referred last year to Iran entering a "zone of immunity," Israeli officials said the phrase referred to the moment when the facility would be complete and immune from attack by Israeli forces. All the centrifuges that enrich uranium at the site have since been installed, but only about a quarter of them are now operating.
The United States has promised Israel $3.1 billion in military financial aid in this fiscal year, the most ever. Mr. Hagel cited the $460 million the United States has already given to Israel for its missile-defense systems and noted the $220 million request for the next fiscal year.
After his meetings in Tel Aviv, Mr. Hagel toured northern Israel by helicopter.