Clare Short "clearly doesn't agree" with Tony Blair on how to proceed in Iraq once war is over, said Tory leader Iain Duncan Smith.
Ms Short had previously threatened to resign
The international development secretary has said that without UN backing, coalition troops would be effectively occupying Iraq post-Saddam.
But the prime minister made it clear on Wednesday that he believed the most important issue was that a new Iraqi regime was representative and respected human rights.
He told MPs: "American and British soldiers have put their lives on the
line, and in some cases given their lives, for the liberation of Iraq and the
disarmament of Saddam Hussein.
"We will obviously have to discuss the details of how we make the handover to
civil administration in Iraq because it is important both to protect our own
troops and make sure, frankly, that they did not give their lives in vain."
He also expressed optimism that international agreement could be hammered out.
That view was echoed by Mr Duncan Smith.
"I've always believed if it's possible it would be a good idea if we had a UN resolution for construction but it's not vital," he told the BBC.
"The important thing, the vital thing, is that reconstruction takes place immediately without any delay and the Iraqi people in the country generally can get itself back on its feet with a proper government.
"There's a huge role for the United Nations and one of the problems you've got ... is that the French and others have scope here to mess up another resolution ... it's difficult to see here how this will work out."
Time for a talk?
Asked about Clare Short's assertion that without UN support coalition troops would effectively become an occupying force, Mr Duncan Smith said there was a discrepancy between her position and that of Mr Blair.
"I think the prime minister will have to discuss that matter with her because clearly it doesn't appear as if the prime minister agrees with Clare Short about what happens after we finish this conflict.
"I leave that very much to the internal discussions between the prime minister and his secretary of state."
Ms Short came close to quitting the cabinet when it emerged that war with Iraq would proceed even without a further UN resolution.
She later changed her mind saying leaving at that point would be "copping out" when Mr Blair had no other option.