US Defence Secretary Robert Gates warned in a secret memo in January that Washington lacked an effective strategy for dealing with Iran's alleged nuclear weapons push, it was reported yesterday.

Citing unnamed government sources, The New York Times wrote that a senior official described it as "a wake-up call" that had sparked efforts in the Pentagon, the White House and the intelligence agencies to develop new options for President Barack Obama.

The memo urged the White House to think about how the United States might contain Iran if it decided to produce a weapon and how to deal with the possibility that nuclear fuel or weapons could be obtained by one of the militant groups Iran supports, the report said.

Options reportedly included a secret military operation against Iran if international sanctions fail.

Asked if the story was accurate, Defence Department spokesman Geoff Morrell told AFP that Gates feels "the President and his national security team have spent an extraordinary amount of time and effort considering and preparing for the full range of contingencies with respect to Iran."

Administration critics suggested that the report provided fresh ammunition to those who condemn what they see as the Obama administration's rudderless security policy.

"I didn't need a secret memo from Mr Gates to ascertain that. We do not have a coherent policy. I think that is pretty obvious," said Republican Senator John McCain, a tough critic of the man he lost to in the 2008 White House race.

"We keep threatening sanctions. For well over a year now, in fact, including the previous administration, we keep threatening. And obviously, we have not done anything that would in any way be viewed effective.

"We have to be willing to pull the trigger on significant sanctions and then we have to make plans for whatever contingencies follow if the sanctions are not effective," Mr McCain, a Vietnam War hero considered a leading voice on defence matters in the US Congress, told the "Fox News Sunday" programme.