WASHINGTON —The head of the IRS said Monday his agency has provided Congress with hundreds of thousands of documents, brushing aside accusations that the IRS has obstructed investigations into the targeting of tea party and other political groups before the 2010 and 2012 elections.

Commissioner John Koskinen was appearing at a rare evening hearing on Capitol Hill to answer questions about lost emails by a key figure in the probe.

Koskinen told the House Oversight Committee in prepared testimony that congressional investigators were informed months ago that Lois Lerner had computer problems back in 2011. Koskinen said emails provided to the committee last fall showed that Lerner’s computer had crashed.

The emails indicate that Lerner had lost some data, though they don’t explicitly say that Lerner’s emails were lost. They were provided to congressional investigators as part of the tea party investigation.

“So it should be clear that no one has been keeping this information from Congress,” Koskinen said in prepared testimony.

The IRS in 2011 lost an untold number of emails to and from Lerner. She is the former head of the division that processes applications for tax-exempt status. The Oversight Committee is investigating the handling of applications from tea party and other political groups.

Koskinen said the IRS inspector general is investigating the lost emails.

“It is not unusual for computers anywhere to fail, especially at the IRS in light of the aged equipment IRS employees often have to use in light of the continual cuts in its budget these past four years,” Koskinen said. “Since Jan. 1 of this year, for example, over 2,000 employees have suffered hard drive crashes.”

Ahead of the hearing, committee Chairman Darrell Issa asked Koskinen to address a series of technical questions about the agency’s email system and its policy for retaining official documents.

The title of the hearing suggests that Issa, R-Calif., already has reached some conclusions. The hearing is called, “IRS Obstruction: Lois Lerner’s Missing Emails.”