Former U.S. Internal Revenue Service Commissioner Douglas Shulman (L-R), IRS Director of Exempt Organizations Lois Lerner and U.S. Deputy Treasury Secretary Neal Wolin take their seats to testify before a House Oversight and Government Reform Committee hearing on targeting of political groups seeking tax-exempt status from the IRS, on Capitol Hill in Washington, May 22, 2013. REUTERS/Jonathan Ernst

By Emily Stephenson

WASHINGTON (Reuters) - The discovery of a trove of thousands of emails reinvigorated a long-running inquiry by U.S. House of Representatives Republicans into the Internal Revenue Service's handling of tax-exempt conservative political groups.

U.S. officials told lawmakers late on Thursday that investigators had found 32,774 emails linked to former IRS official Lois Lerner, a key figure in a scandal that broke in 2013. But the emails' importance was still unclear.

More than a year-and-a-half ago, Republicans accused the IRS of unfairly treating conservative groups in reviewing their applications for tax-exempt status. Congressional investigators quickly focused on Lerner, who led the IRS tax-exempt unit.

Lerner, who resigned from the tax agency, refused to testify to a congressional committee about the affair. Republicans voted last May to hold her in contempt of Congress.

In June, the IRS said that some of Lerner's emails had been lost in a computer hard-drive failure. The U.S. Justice Department said it was investigating.

At a congressional hearing on Thursday evening, Timothy Camus, a Treasury deputy inspector general for tax, told lawmakers that it was not clear whether any of the new trove of emails recovered by his group contained new information.

Camus did not describe the content of the emails, which were located on backup tapes at a West Virginia facility. He said investigators are trying to determine whether additional backup tapes exist that may contain more of Lerner's emails.

Republicans seized on the discovery as evidence that the IRS, which declared the emails missing last year, has been lax in cooperating with the congressional probe.

"I've got to tell you, we have been patient, we have asked, we have issued subpoenas, we have held hearings," said Representative Jason Chaffetz, a Utah Republican who leads the House Oversight Committee.

"It's just shocking to me that you start (looking), two weeks later you're able to find the emails," he told Camus, referring to the Treasury inspector general's office locating the emails after the IRS said it could not find them. The IRS is part of the Treasury Department.

Democrats on the panel argued that the hearing was premature and politically driven. Representative Carolyn Maloney, a New York Democrat, said it was not yet clear whether the recovered emails contained any new material.

(Reporting by Emily Stephenson; Editing by Kevin Drawbaugh and Jonathan Oatis)