WASHINGTON - The US congressman heading an investigation into a botched gun-trafficking case said on Sunday he had no evidence the White House was involved in a cover-up about the operation or in providing misleading information to Congress.

However, Republican Representative Darrell Issa said documents the White House was shielding under an executive privilege claim would shed more light on how much high-level officials knew about a misleading February 4, 2011 letter to Congress denying that guns had been allowed to "walk" into the hands of Mexican drug cartels.

Republicans, who control the House of Representatives, have suggested that some sort of a cover-up of information explained why it took until December 2011 for the Justice Department to formally withdraw the letter about the case, which was named "Operation Fast and Furious."

The House is set to vote this week on contempt of Congress charges against US Attorney General Eric Holder, the top US law enforcement official, for withholding access to some of those documents.

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