The White House on Friday accused Republican lawmakers of propagating unfounded claims over the loss of former IRS official Lois Lerner's emails regarding the IRS targeting of conservative political groups.

White House spokesman Josh Earnest said the White House opposed appointing a special prosecutor to investigate the missing email controversy.

"I think that many Republicans in Congress, at least, particularly in the House, have demonstrated a pretty aggressive appetite for investigating this issue," Earnest said.

"There have been a large number of claims and conspiracy theories that have been floated about this process by Republicans that just have not panned out, frankly."

Earlier Friday, IRS Commissioner John Koskinen denied that his agency was covering up or had deliberately lost Lerner's correspondence. The IRS has said a hard drive containing Lerner's emails from 2009-2011 crashed, and the equipment was subsequently recycled and destroyed.

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That evoked a stinging rebuke from House Ways and Means Committee Chairman Dave Camp (R-Mich.), who said the "American people have no reason to trust the IRS or, frankly, the administration on this issue."

"You say that you have ‘lost’ the emails, but what you have lost is all credibility,” Camp said.

But Earnest said that "13 months of multiple congressional investigations" have not "turned up any facts that support the conspiracy theories that they've propounded."

"These are investigations that have a pretty transparent political motive," Earnest said. "So I'm not sure that there's a whole lot more to be discovered here."

The White House spokesman also noted House Oversight Committee Chairman Darrell Issa Darrell Edward IssaDCCC reserves new ad buys in competitive districts, adds new members to 'Red to Blue' program Wife of former Rep. Duncan Hunter sentenced to 8 months of home confinement Harris endorses Democrat in tight California House race MORE (D-Calif.) said in a 2008 committee hearing that "archiving in the digital age is not as easy as it might seem."

And, Earnest said, the agency's inspector general did not find evidence of inappropriate targeting.

"Frankly, we'd prefer it if Republicans would devote this kind of attention and energy to policies that are actually going to create jobs, as opposed to partisan fishing expeditions," Earnest said.

Earlier this week, the White House said it found no relevant emails between the White House and Lerner during the relevant time period. Some have suggested the White House might have ordered Lerner to target the conservative political group.