Iran in US sights over its nuke ambition

But barely had the White House declared Iran its number one threat, than Tehran said it was willing to talk to its arch-enemy over Iraq, currently teetering on the brink of all-out civil war.

Washington, which once branded Iran as part of an "axis of evil" with North Korea and Saddam's Iraq, has been piling the pressure on Tehran over its nuclear programme and accusing it of meddling in Iraq.

The White House this week bluntly warned both Iran and North Korea that it would take preemptive military action if necessary to protect itself, making no apologies for the war in Iraq.

"We may face no greater challenge from a single country than from Iran," the White House said in a blueprint called the "National Security Stategy" obtained by AFP on Thursday.

Washington has been spearheading the international campaign against Iran over its nuclear power efforts, which the United States claims is a cover for efforts to develop atomic weapons -- charges vehemently denied by Tehran.

President George W. Bush had made Saddam's alleged possession of chemical and biological weapons and pursuit of nuclear arms the centrepiece of his case for war, but no such weapons have been found.

"There will always be some uncertainty" about banned weapons programmes, the White House said. "We have no doubt that the world is better of if tyrants know that they pursue WMD at their own peril."