U.S. Secretary of Defense Leon Panetta said Monday that Iran will have a nuclear weapon within one year, if not less.

Speaking in an interview with CBS Evening News, Leon Panetta said that it would probably take a year for Tehran to assemble a nuclear bomb, but said that one provision is if the Iranians have a hidden facility that "may be enriching fuel."

Panetta said Israel's concern for a nuclear Iran is a "common concern" of the U.S., and that Washington would not rule out a military attack.

"The United States does not want Iran to develop a nuclear weapon. That's a red line for us and that's a red line, obviously, for the Israelis," he told CBS.

"If they (Iran) proceed and we get intelligence that they are proceeding with developing a nuclear weapon then we will take whatever steps necessary to stop it."

When asked by CBS whether the U.S. would consider taking military steps, Panetta said, "There are no options off the table," and added that a nuclear Iran is "unacceptable".

According to CBS, Panetta added that, while the Iranians need a year or less to assemble a weapon, he has no indication yet as to whether they have decided to pursue that path.

Earlier this month, Panetta sent a clear message that Israel should not consider unilateral action against Iran. Speaking on December 2 at Washington's Saban Center for the Middle East, Panetta said the key to effective action against Iran's nuclear ambitions was close cooperation between allies.

Panetta's words echoed a similar message delivered during a recent visit to Israel, in which he stressed that any military operation against Iran by Israel must be coordinated with the United States and have its backing. "There is always a military option," he said, "but it must be the last resort, not the first."

In response, Israeli Defense Minister Ehud Barak said Panetta's full message is more complex than what he presented in that speech. "We are in constant dialogue with the Americans," he said, adding, "I've met Panetta about a dozen times over the last two or three years. In person we hold more intensive talks."

Barak said the entire international community agrees the diplomatic course should be pursued and use of sanctions must be exhausted, yet, he added that "no option should be taken off the table. Israel is responsible for its security, its future and its existence."

On Friday December 16, Barak met with U.S. President Barack Obama prior to the latter's remarks at the General Assembly of the Union for Reform Judaism in Maryland. He has also spoken to the top diplomatic and military leadership in the Obama administration over the past several weeks, including Secretary of State Hillary Clinton, National Security Adviser Tom Donilon, as well as Panetta.

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