White House aide Karl Rove has appeared for the fourth time before the grand jury investigating the leaking of the identity of a covert CIA agent.
The investigation is expected to finish at the end of this month
Mr Rove's lawyer said that prosecutors had told his client no decision had yet been made about possible charges.
He has said his client was happy to co-operate with the probe.
The identity of CIA agent Valerie Plame was revealed by a journalist in 2003. Her husband is a former diplomat who criticised President Bush over Iraq.
It was alleged that a White House source leaked Ms Plame's identity to "punish" or discredit her husband for his criticism.
The White House had long maintained that Mr Rove had nothing to do with the leak, but reporters have since said he talked about the agent, although not by name.
Mr Rove's lawyer, Robert Luskin, says his client was not part of "any scheme to punish Joe Wilson by disclosing the identity of his wife".
Prosecutors are close to the end of the inquiry.
Mr Rove made no comment as he entered and left the courthouse for his fourth appearance before the commission, which took place behind closed doors.
Mr Rove spent about four-and-a-half hours inside the courthouse.
"The special counsel has not advised Mr Rove that he is a target of the investigation and affirmed that he has made no decision concerning charges," Mr Luskin said.
"The special counsel has indicated that he does not anticipate the need for Mr Rove's further co-operation," he said.
Correspondents say that prosecutor Patrick Fitzgerald has a variety of options as he weighs whether anyone broke a law that bars the intentional unmasking of a covert CIA officer.
Some defence lawyers in the case believe Mr Fitzgerald might pursue other possible charges, such as making false statements, obstruction of justice or mishandling of classified information, the Associated Press reports.
Prosecutors have told Mr Rove they cannot guarantee he will not be indicted.
Mr Rove played a key role in formulating the president's successful election strategy last year.
If he was charged, it would be seen as a huge blow to President Bush, correspondents say.
Mr Rove is a vital link between the President and the various groups and individuals who form the backbone of Mr Bush's support.
The problem for the White House is that the Rove issue comes on top of Hurricane Katrina, Iraq, rising petrol prices and a general sense of unease among Americans about the way they are being governed, says the BBC's Justin Webb, in Washington.
In the latest opinion poll, only just over a quarter of people questioned believe that in the long run the Bush presidency will be seen as a success.