Mr Cohen said Washington would prefer to take action against Iraq in concert with the United Nations and its allies, but a unilateral American attack "has always been an option that we could pursue".
Undaunted by threats, Iraq said it would not back down from its decision to ban UN weapons inspectors from working in the country.
"We are not afraid of threats or any other reaction," the Deputy Prime Minister, Tariq Aziz, said in Baghdad.
The crisis escalated when Iraq cut off all dealings with UN arms inspectors on Saturday. The Security Council immediately condemned the move as "a flagrant violation" of UN resolutions.
The US will have difficulty persuading its allies that air strikes will succeed where they have failed before in getting Iraq to co-operate.
Of the other permanent members of the Security Council, China, Russia and France want to move faster on removing sanctions against Baghdad. Only Britain and the US are adamant that they must stay until every issue has been cleared up.
The Iraqi move came after the UN launched a review of Baghdad's compliance with UN resolutions without a clear guarantee that sanctions would be lifted, at US insistence.
The standoff comes days ahead of the US Congressional elections. The Republicans are likely to use the issue once again to beat the White House.Reuse content