JERUSALEM -- For more than a decade, Israel has systematically built up its military specifically for a possible strike on Iranian nuclear facilities. It has sent its air force on long-distance training missions, procured American-made "bunker-busting" bombs and bolstered its missile defenses.

Prime Minister Benjamin Netanyahu's threats to strike Iran, voiced last week during a high-profile visit to the White House, were not empty bluster.

Although a unilateral Israeli attack would probably not destroy Iran's nuclear program, it appears capable, at least for now, of inflicting a serious blow.

"If Israel attacks, the intention is more to send a message of determination, a political message instead of a tactical move," said Yiftah Shapir, a former Israeli air force officer who is now a military analyst at the INSS think tank in Tel Aviv.

Israel, along with the United States and other Western countries, believes Iran has taken key steps toward developing nuclear weapons. The UN's nuclear watchdog agency has cited this concern, but notes its inspectors have found no direct evidence that Iran is moving toward an atomic weapon.

Israeli leaders, however, argue that time is quickly running out. They have grown increasingly vocal in their calls for tough concerted international action against Iran while stressing they are prepared to act alone if necessary.

Israeli defense officials believe Iran is capable of producing highly enriched weapons-grade uranium within six months. After that, it would require another year or two to develop a means of delivering a nuclear bomb, they predict.

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But Israel believes the window to act will close much sooner than that. Officials say in the coming months Iran will have moved enough of its nuclear facilities underground and out of reach of conventional airpower, and that the world will be powerless to stop it.

Defense Minister Ehud Barak calls this the "zone of immunity." Defense officials acknowledge that plans to go after Iran have been in the works for years, with the air force expected to take the lead in what would be an extremely complicated operation. The officials spoke on condition of anonymity because they were discussing sensitive military deliberations.