The US Treasury Department has called for an investigation into whether its former head leaked secret documents in a new book.
O'Neill has been out of the Administration for two years
Former Treasury Secretary Paul O'Neill appeared on a US news programme to promote the book in which documents marked "secret" were shown.
A Treasury department spokesman said it had asked its inspector general to see if disclosure laws were violated.
Mr O'Neill was sacked from the US Government in December 2002.
BBC Washington correspondent Justin Webb says that despite a statemanslike response from President George W Bush, the reaction behind the scenes has been vitriolic.
Our correspondent says that the episode is a reminder that not all senior Republicans think Mr Bush has made the right choices at home or abroad.
Responding to Mr O'Neill's comments - which come a week before Mr Bush is due to make his annual State of the Union address - the US president said that, as with previous US administrations, he had been for regime change in Iraq.
However, he suggested, the task had only become urgent after the terror attacks on America in September 2001.
Mr O'Neill made the statements in an interview with the CBS "60 Minutes" news programme on Sunday.
He has contributed to a book on the Bush administration called The Price of Loyalty by journalist Ron Suskind, for which the former secretary provided thousands of documents for research purposes.
Treasury Department spokesman Rob Nichols said that, although it was customary for officials to take documents when they left office, a document marked as secret was shown on the programme.
He said the proposed probe would focus on how possibly classified information appeared on television and the inspector general could then "take appropriate steps, if necessary", he was quoted by Reuters news agency as saying.
Mr O'Neill accused Mr Bush of planning for an invasion of Iraq within days of coming to office, saying the US president was looking for an excuse to oust Saddam Hussein.
He added that, as a member of the US president's national security team, he never saw any evidence of Iraqi weapons of mass destruction.
Mr O'Neill also gave an unflattering account of Mr Bush's leadership style in the interview, saying that at cabinet meetings the president was like a blind man in a room full of deaf people.
Mr O'Neill was sacked from the US Government after nearly two years in his position over differences with the Bush administration.
But the current Commerce Secretary, Don Evans, told CNN that the president liked nothing better than vigorous discussion in cabinet.
"He drives the meetings, tough questions, he likes dissent, he likes to see debate," he said.
Republican Representative Mark Foley of Florida also accused Mr O'Neill of delivering a "blatant stab in the back".