Dick Cheney, the US vice-president, insisted on Sunday that ongoing violence only reflects "desperation" by al-Qaida, which is attempting to spark internecine conflict.
His remarks followed widely publicised comments on Sunday by former Iraqi premier Iyad Allawi that the country had already plunged into civil war.
"Clearly there is an attempt underway by the terrorists, by Zarqawi and others to foment civil war," Cheney said, referring to al-Qaida in Iraq leader Abu Musab al-Zarqawi.
"That's been their strategy all along, but my view would be they've reached a stage of desperation ... They are doing everything they can to stop the formation of a democratically elected government."
"I don't think they've been successful," Cheney said.
General George Casey, commander of US military forces in Iraq, argued on Sunday that an Iraq civil war was neither "imminent" nor "inevitable".
"I personally don't believe ... that we're there now," he said, referring to civil war.
"I believe that as the leadership of this country comes forward, forms the government of national unity and that begins to move forward, I believe you'll gradually see these tensions ebb," he said on Fox News Sunday.
Casey later told CNN that, "by our most pessimistic estimates", less than 0.1% of the Iraqi people are involved in the insurgency.
On Sunday, a Newsweek magazine poll showed that popular approval of Bush's handling of Iraq plummeted to 29% while those who disapprove of his Iraq policy shot up to 65%.
A Wall Street Journal/NBC News poll on Thursday put Bush's overall approval ratings at 37%.
Bush defended the invasion decision on Saturday and insisted that things were improving in Iraq.
"It may seem difficult at times to understand how we can say that progress is being made," Bush said in his weekly radio address.
"We will finish the mission. By defeating the terrorists in Iraq, we will bring greater security to our own country."