New York: Acknowledging for the first time that he "miscalculated" post-war conditions in Iraq, US President George W Bush has said the continuing insurgency was the product of a "swift victory" against ousted dictator Saddam Hussein's military.

"The 17-month-long insurgency that upended the administration's plans for the country was the unintended by-product of a swift victory against Saddam Hussein's military which fled and disappeared into the cities, enabling them to mount a rebellion against the US forces far faster than anticipated," Bush said in an interview to 'New York Times'.

Bush said that his strategy had been "flexible enough" to respond, and said that even now "we're adjusting to our conditions" in places like Najaf, where American forces have been battling one of the most militant of the Shiite groups opposing the American-installed Government.

The daily said Bush refused to go into further details on what went wrong with the occupation, suggesting that such questions should be left to historians.

He also joined issue with his Democratic challenger John Kerry's argument that Bush administration's focus on Iraq had given North Korea the opportunity to significantly expand its nuclear capability.

"Showing none of the alarm about the North's growing arsenal that he once voiced regularly about Iraq," the Times says, "Bush opened his palms and shrugged" when an interviewer asked that new intelligence reports had indicated that North Korea may now have the fuel to produce six or eight nuclear weapons.