Washington (CNN) The IRS watchdog investigating the disappearance of Lois Lerner's emails told a Senate committee it has found roughly 6,400 messages that have never before been turned over to Congress.

Lerner was the IRS official at the center of allegations that the agency targeted tea party groups applying for nonprofit status. Congress requested Lerner's emails from the IRS and agency officials told lawmakers an unknown number of emails had been lost when Lerner's computer crashed.

The Treasury Inspector General for Tax Administration is in the process of turning the emails over to the Senate Finance Committee, which is investigating whether the IRS wrongly targeted conservative and other groups seeking tax-exempt status, committee spokesman Aaron Fobes said.

"These emails will be carefully examined as part of the committee's bipartisan IRS investigation," he said.

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