White House withholds Fast and Furious files
President Obama has taken the rare step of asserting executive privilege to withhold documents sought by lawmakers probing a botched US sting operation.
The attorney general is facing moves to hold him in contempt of Congress over the issue.
Justice officials said the privilege applied to files on how they learned of problems with Fast and Furious.
The operation saw US agents lose track of hundreds of illegal guns allowed into Mexico to trace arms dealers.
A US border agent was killed with a weapon linked to the operation in December 2010.
This is the first use of executive privilege for withholding documents by Mr Obama. Former Presidents George W Bush and Bill Clinton used the privilege six and 14 times respectively during their eight-year terms.
The Department of Justice says it has denied access to the files because they contain information that could affect ongoing criminal investigations.
Its officials say they have already sent more than 7,000 documents to the Republican-led House Oversight Committee.
"I write now to inform you that the president has asserted executive privilege over the relevant... documents," Deputy Attorney General James Cole wrote to the lawmakers.
Wednesday's contempt vote looms a day after a meeting between Attorney General Eric Holder and committee chairman, Representative Darrell Issa, failed to end the impasse.
Mr Holder said lawmakers had turned down his offer to give them the documents, along with a briefing on the operation, in exchange for assurances that the panel would drop contempt proceedings.
"They rejected what I thought was an extraordinary offer on our part," he told reporters on Tuesday.
But Republican Senator Charles Grassley, who is not on the committee but attended the meeting, cast doubt on Mr Holder's version.
"The attorney general wants to trade a briefing and the promise of delivering some small, unspecified set of documents tomorrow for a free pass today," he told reporters.
On Wednesday, the office of Republican House Speaker John Boehner said use of executive privilege raised questions about the White House's involvement with the gun probe.
"The White House decision to invoke executive privilege implies that White House officials were either involved in the 'Fast and Furious' operation or the cover-up that followed," Brendan Buck, a spokesman for Mr Boehner, told reporters.
The committee's top Democrat, Representative Elijah Cummings, accused Mr Issa of having "no interest" in resolving the dispute.
"You've been holding the attorney general to an impossible standard," he told CNN.
"You accused him of a cover-up for protecting documents that he is prohibited from providing."
It is not clear what will happen if Mr Holder is held in contempt of Congress.
Historically, Congress and the White House have negotiated agreements to avoid a court battle that would limit either Congress' subpoena power or executive privilege itself.