Former US secretary of state Henry Kissinger said in an interview Sunday that the United States should assume that Iran is actively preparing to build nuclear weapons.

Kissinger, 88, was asked on the CNN show "GPS" if the threat of an Iranian nuclear weapon was so dire that Israel would need to launch a military strike in the near future.

"I am very uneasy with the so-called intelligence report that say we don't know whether they are actually working on nuclear weapons," Kissinger told CNN.

"I think we should start from the premise that they are undergoing all this in order to achieve a military capability. I don't think that is a disputable point."

US intelligence analysts believe there is no hard evidence that Iran has decided to build a nuclear bomb -- an assessment broadly consistent with a 2007 intelligence finding that concluded that Iran had abandoned its nuclear weapons program, The New York Times reported in February, citing unnamed US officials.

The assessment was largely reaffirmed in a 2010 National Intelligence Estimate, and that it remains the consensus view of America's 16 intelligence agencies, the Times reported.

The US administration maintains that tough sanctions on Iran and diplomatic efforts need to be given more time before any resort to bombing raids.

Israeli leaders however say time is running out for any pre-emptive strike. Prime Minister Benjamin Netanyahu said on Monday that sanctions against Iran have not worked, and "none of us can afford to wait much longer."

US President Barack Obama has cautioned against "bluster" in talking about possible war with Iran, saying there still exists a window of diplomacy.