America's defence chiefs have adopted a belligerent new tone over the possibility of carrying out a military strike against Iran.

In an interview with CBS on Monday, Secretary of Defence Leon Panetta said that the Iranians are at a point in the their nuclear programme where they can develop a bomb in a year or less.

He added that the Obama administration "shares the same concern" with Israel over the Iranian nuclear programme and that an Iranian bomb would be "unacceptable".

According to Mr Panetta, "the US 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. If we have to do it we will deal with it."

The Defence Secretary would not specify whether the US is planning a military strike but emphasised that "there are no options off the table".

The head of the US military, Chairman of the Joint Chiefs of Staff General Martin Dempsey, was more specific in an interview with CNN on Tuesday.

He said that a military strike would be "executable if necessary", though he warned of a "miscalculation" that could cause "a tragedy for the region and for the world".

General Dempsey acknowledged that should Israel decide to attack Iran, there was no guarantee that it would give the US prior warning and that the US military was co-operating with the IDF to "establish some confidence on the part of the Israelis".

These forthright statements by Mr Panetta and General Dempsey signal a change in the US position. Previously, the American intelligence community believed that Iran was a few years away from assembling a nuclear bomb and Mr Panetta himself has warned against a military strike in recent months.

Senior officials in the Israeli defence establishment connected the shift in American policy to new intelligence passed on last week in meetings in Washington between Defence Minister Ehud Barak, President Barack Obama, National Security Adviser Tom Donilon, Mr Panetta and other senior American officials.