President Bush last night insisted he would withhold judgment on the role of senior political adviser Karl Rove over a controversy in which he is alleged to have leaked a CIA agent's identity.
Mr Bush said there was a "serious" federal investigation under way into who leaked the identity of covert CIA agent Valerie Plame and that he would not prejudge the outcome.
Mr Bush last night stopped short of issuing a public vote of confidence in Mr Rove, as some Republicans had expected.
Mr Bush's comments come after Timemagazine journalist Matthew Cooper identified Mr Rove as a source, saying he had testified under a "waiver agreement with Karl Rove's attorney."
New York Timesreporter Judith Miller refused to testify about sources she spoke to on the story and was jailed.
Mr Rove's lawyer, Robert Luskin, said in a statement that his client "has been repeatedly assured he is not a target of the investigation" by a special prosecutor into the leak.
Some prominent Democrats have called on the president to fire Mr Rove, the architect of his two presidential election victories and now his deputy chief of staff, or block his access to classified information.
Ms Plame's husband, diplomat Joseph Wilson, said the leak was meant to discredit him for criticising Mr Bush's Iraq policy in 2003 after a CIA-funded trip to investigate whether Niger helped supply nuclear materials to Baghdad.