Official Jerusalem struck back at the US Monday for saying it would not set clear red lines beyond which it would support a military attack on Iran’s nuclear facilities.

“Words like these won’t stop the centrifuges, but the opposite,” an unnamed source said.

On Sunday, US Secretary of State Hillary Clinton rebuffed calls by Prime Minister Benjamin Netanyahu to set clear red lines and calm Israeli fears.

Asked if the Obama administration will lay out sharper “red lines” for Iran or state explicitly the consequences for Tehran of its failing to negotiate a deal with world powers over its nuclear program by a certain date, Clinton told Bloomberg, “We’re not setting deadlines.”

“We’re watching very carefully about what they do, because it’s always been more about their actions than their words,” Clinton said in an interview following visits to China and Russia, where she spoke with leaders of both countries to seek cooperation on Iran.

On Monday, State Department spokeswoman Victoria Nuland reiterated Clinton’s statement, saying setting red lines was “not useful.”

“So, you know, we are absolutely firm about the president’s commitment here, but it is not useful to be parsing it, to be setting deadlines one way or the other, red lines,” she said.

Israeli sources said the US refusal would detract from the credibility of the threat that Iran could come under military attack if it doesn’t abandon its program.

“Without a firm and clear red line, Iran won’t stop its race for a nuclear weapon,” a source said. “Words like these don’t only not deter Iran, they calm it.”

However, Defense Minister Ehud Barak said Monday that Israel would not embark on a military strike unless all other options had been exhausted.

“The political echelon sees as its responsibility ensuring that if there is a way to reject war, that it be done, and we confirm that if we go to war this will only be after all other possibilities have been exhausted,” Barak said at a New Year’s ceremony at the Tel Nof air base in central Israel.  Israel Defense Forces Chief of General Staff Benny Gantz was also in attendance.

The possibility of the US announcing its “red lines” on Iran had appeared to be playing a role in calming tensions in the last few days between Israel and the US, which have been publicly at odds in recent weeks over how best to halt the Islamic republic’s nuclear drive.

Last week, after The New York Times reported that the administration was considering setting out certain red lines that, if crossed by Iran in its nuclear drive, would trigger a resort to military force, Netanyahu welcomed the idea. “The greater the resolve and the clearer the red line, the less likely we’ll have conflict,” he said.