Media playback is unsupported on your device Media caption "An unnecessary court conflict will ensue"

US Attorney General Eric Holder has been held in contempt of Congress for refusing to hand over a set of files on a failed gun-running investigation.

In a 255-67 vote, 17 Democrats joined with the House of Representatives' Republican majority.

Mr Holder is the first sitting attorney general and US presidential cabinet member to be held in contempt.

The White House has refused to hand over files outlining how problems with Fast and Furious emerged.

The operation saw US agents lose track of hundreds of illegal guns sold in Arizona and allowed into Mexico to target dealers.

Two of the weapons were found in December 2010 at the scene of a US border agent's murder. Fast and Furious ended in early 2011.

'Political game'

Mr Holder told reporters that the vote was "misguided" and said lawmakers had been circulating "truly absurd" conspiracy theories.

"It will not distract me from the important tasks that are our responsibility," Mr Holder said.

Image caption Dozens of House Democrats, including leader Nancy Pelosi, walked out

The House also voted 258-95 to ask the courts to force Mr Holder to turn over the documents.

Many Democratic lawmakers, including the Congressional Black Caucus and Democratic leader Nancy Pelosi, walked out of the chamber in protest on Thursday.

"We don't want to play a part in this political game," Democratic Representative Gregory Meeks said.

The roots of the current Congressional investigation began on 4 February 2011 when the justice department sent lawmakers a letter denying they had sanctioned or otherwise knew about guns illegally ending up Mexico.

The department withdrew the letter 10 months later, acknowledging the operation had allowed guns across the border.

Led by Republican Darrell Issa, the House Oversight Committee subpoenaed documents for the 10-month period.

The Department of Justice says it has denied access to the files because they contain information that could affect ongoing criminal investigations.

Demand for answers

Mr Issa did not accept an offer of files and a briefing on the operation, saying the department needed to hand over all the documents requested.

Image caption Eric Holder spoke to a civic group in Florida before the contempt vote

The justice department sent to the House Oversight Committee more than 7,000 documents relating to Fast and Furious, and to a similar operation that took place during the George W Bush administration.

Last week, the White House raised the stakes by announcing it would exert executive privilege to protect the documents in question from subpoena.

The National Rifle Association has told House members that it will include the contempt vote in ratings the lobby group uses to show how lawmakers align with its interests.

Dan Pfeiffer, White House communications director, called the vote a "transparently political stunt" that happened despite justice department efforts to accommodate Congress.

Republican leaders defended the vote. House Speaker John Boehner said during the House debate that "no justice department is above the law".

"A man died serving his country and we have a right to know what the federal government's hand was in that," said Republican lawmaker Rich Nugent.