The top US military officer told Reuters on Wednesday he did not know whether Israel would alert the United States ahead of time if it decided to take military action against Iran.
General Martin Dempsey, the chairman of the Joint Chiefs of Staff, also acknowledged differences in perspective between the United States and Israel over the best way to handle Iran and its nuclear program.
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He said the United States was convinced that sanctions and diplomatic pressure was the right path to take on Iran, along with "the stated intent not to take any options off the table" - language that leaves open the possibility of future military action.
"I'm not sure the Israelis share our assessment of that. And because they don't and because to them this is an existential threat, I think probably that it's fair to say that our expectations are different right now," Dempsey said in an interview as he flew to Washington from London.
Asked whether he was talking about the differences between Israeli and US expectations over sanctions, or differences in perspective about the future course of events, Dempsey said: "All of the above." He did not elaborate.
He also did not disclose whether he believed Israel was prepared to strike Iran.
Iran is facing new sanctions after the International Atomic Energy Agency (IAEA) reported earlier in November that Tehran appeared to have worked on designing a bomb and may still be conducting secret research to that end.
Iran says its nuclear program is peaceful.
The sanctions push got added momentum on Wednesday as diplomatic sources said Britain would support an embargo on Iranian oil imports. But Iran sees its nuclear program as a source of power and prestige and it is unclear whether sanctions will alter its cost-benefit analysis.
There has been concern that if world powers cannot nudge Iran into serious nuclear negotiations, then Israel, which feels threatened by Iranian nuclear aspirations, will attack.
Asked directly whether Israel would alert the United States ahead of time if it chose to go forward with military action, Dempsey replied flatly: "I don't know."
Last week, US Defense Secretary Leon Panetta raised American concerns
about the unintended consequences of any military action against Iran
during talks with his Israeli counterpart, Ehud Barak, at a security
forum in Canada.
Those included US fears about fallout on the world economy and that a
strike would only delay - not derail - Iran's nuclear program.
Iran has warned that it will respond to any attacks by hitting Israeli
and US interests in the Gulf. Analysts say Tehran could retaliate by
closing the Strait of Hormuz, the waterway where about 40 percent of all
traded oil passes.
Dempsey, who took over the Pentagon's top uniformed position in
September, said there were no new arguments the United States was about
to pose to Israel on the matter. Instead, he cited US and Israeli
efforts to "consistently try to update each other on the existing