Gregory Korte and Fredreka Schouten

USA TODAY

WASHINGTON -- House Republicans stepped up their investigation of the Internal Revenue Service on Monday after the tax agency said it lost copies of more than two years worth of e-mails at the center of a congressional probe.

The missing e-mails have rekindled a 13-month-old controversy over the IRS' treatment of conservative groups. The IRS says a computer crash destroyed e-mails to and from former Exempt Organizations Director Lois Lerner during the time period when the IRS was first starting to hold up tax exemption applications from Tea Party groups.

Ways and Means Committee Chairman Dave Camp, R-Mich, said Monday that House Republicans were "simply not going to accept the IRS claim that these documents are not recoverable." He called on the Obama administration to order the release of any e-mails Lerner may have sent to the White House or other agencies.

Speculation about those e-mails is "indicative of the kinds of conspiracies that are propagated around this story," White House spokesman Josh Earnest said aboard Air Force One as President Obama returned from a West Coast trip Monday. "And they're propagated in a way that has left people with a very mistaken impression about what exactly occurred."

The IRS said Lerner's computer hard drive crashed in 2011, destroying local copies of e-mails she sent and received between January 2009 and April 2011. Regardless, the IRS said it was able to recover 24,000 e-mails from that time period through other sources, and it has already turned them over as part of the 67,000 e-mails it's turned over to Congress.

IRS Commissioner John Koskinen agreed Monday to testify to two House committees about the e-mails: the Oversight and Government Reform Committee on June 23 and the Ways and Means Committee on June 24.

Last month, the House voted to hold Lerner in contempt of Congress for refusing to answer lawmakers' questions. The Justice Department is investigating whether any laws were broken by IRS officials.