"As you go upscale from snowball to weapons of mass destruction, at some point where the risk gets high enough it's not going to be a snowball in your face," he said.

"It could be a biological weapon that is going to kill tens of thousands of human beings. Then you have to ask yourself if you have an obligation to take the blow and do something afterwards."

Rumsfeld acknowledged an assertion that the US image in the world had been hurt but blamed it on media coverage, which he called "shocking, absolutely shocking."

"To think what was going on in Iraq a year ago with people being tortured, rape rooms, mass graves, gross corruption, a country that had used chemical weapons on its own people, used them on their neighbors, defiant to the United Nations through 17 security council resolutions," he said.