The US White House has rejected subpoenas for documents relating to the case of federal prosecutors sacked last year, citing executive privilege.
Congressional committees had asked for the papers to be submitted by Thursday.
This comes a day after the Senate demanded White House documents linked to its domestic spying programme.
Tensions with the White House have been building since Democrats took control of Congress in January and vowed to hold the administration to account.
Internal communications
Presidential counsel Fred Fielding said in a letter to the Senate and House of Representatives judiciary committees that he regretted no compromise had been found.
"Increasingly, the president and vice president feel they are above the law - in America no-one is above law"
"We had hoped this matter could conclude with your committees receiving information in lieu of having to invoke executive privilege. Instead, we are at this conclusion," he wrote.
Mr Fielding said the administration had tried to co-operate with the investigation by releasing more than 8,500 pages of documents and sending some senior officials to testify.
But he said President George W Bush was not prepared to release documents revealing internal White House communications.
He also said that former presidential counsel Harriet Miers and former political director Sara Taylor would not testify in the case next month, as directed by the subpoenas.
US ATTORNEYS
Senate judiciary committee chairman Patrick Leahy responded by accusing the administration of "Nixonian stonewalling" - a reference to former President Richard Nixon's frequent use of executive privilege to block Senate subpoenas.
"Increasingly, the president and vice president feel they are above the law - in America no-one is above law," Mr Leahy said in a statement.
"This White House cannot have it both ways. They cannot stonewall congressional investigations by refusing to provide documents and witnesses, while claiming nothing improper occurred."
Correspondents say the judiciary committee's demands are partly designed to embarrass the White House, but the committee will now be closely watched to see how it responds.
Gonzales row
The row over the firing of eight federal US attorneys in 2006 has been building for several months.
Congress Democrats have been trying to force the resignation of Attorney General Alberto Gonzales, accusing him of firing the prosecutors for political reasons and then lying about the reason for their dismissal.
Some Republicans have also backed the moves.
But the president has dismissed the attempts to remove Mr Gonzales as themselves political.
White House officials say this is only the second time Mr Bush has invoked executive privilege.
The first was in December 2001, when Congress sought documents from the Clinton administration.
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