"We suspect they are probably already working on warheads for ground-to-ground missiles," Barak said in an interview with The Washington Post and Newsweek magazine.

He also suggested that Iranians "probably ... have another clandestine enrichment operation beyond the one in Natanz."

The remarks were in stark contrast the conclusion of a US National Intelligence Estimate released late last year that said Tehran had abandoned its quest for nuclear weapons as far back as 2003.

Barak sharply disagreed with this assessment.

"Our interpretation is that clearly the Iranians are aiming at nuclear capability," he said. "It's probably true that ... they may have slowed down the weapons group in 2003, because it was the height of American militarism."

But he said Israel now believed that Iranians "are quite advanced, much beyond the level of the Manhattan Project."

He did not elaborate.

The World War II-era Manhattan Project helped the United States develop the nuclear bombs that were dropped in August of 1945 on the Japanese cities of Hiroshima and Nagasaki.

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