The White House has said that an international diplomatic effort to force Iran to give up its nuclear ambitions must succeed 'if confrontation is to be avoided'.
In a new national security strategy document, the Bush Administration says that the United States may face no greater challenge from a single country than from Iran.
It also described national security challenges in Iraq and across the Middle East, as well as in Russia and China.
The US and its European allies are continuing to investigate suspicions that Tehran is trying to develop a nuclear weapons programme despite its insistence that it merely wants atomic power for civilian use.
US President George W Bush has insisted on a diplomatic outcome to the negotiations but has never taken the military option off the table, although experts believe US involvement in the Iraq war is a limiting factor.
