WASHINGTON (Reuters) - A judge told the U.S. Internal Revenue Service on Thursday it must submit an explanation by Aug. 10 for how it lost emails being sought in a Republican congressional inquiry of a 2013 controversy over tax scrutiny of conservative political groups.

U.S. District Judge Emmet Sullivan also appointed a federal magistrate to look into possibilities of recovering any of the lost emails, sent to and by Lois Lerner (pictured above), a former senior IRS official who was involved in the controversy.

Sullivan's order came after a hearing on a lawsuit seeking the emails under the Freedom of Information Act brought by Judicial Watch, a conservative activist group.

"Judge Sullivan also authorized Judicial Watch to submit a request for limited discovery into the missing IRS records after Sept. 10," said Judicial Watch President Tom Fitton in a statement distributed after the hearing.

An IRS spokesman declined to comment, citing the agency's policy against discussing pending litigation.

Republicans have been investigating the IRS's extra scrutiny of conservative groups seeking tax-exempt status since the agency's practice burst into view in May 2013. That was when Lerner publicly apologized for it at a conference.

Her unexpected statement triggered the worst crisis at the IRS in years, with Republicans accusing the agency of singling out conservative groups, some aligned with the Tea Party, for unfair treatment. Lerner retired from the IRS in September.

The issue had faded from view until last month when the IRS said it lost some of Lerner's emails, which Republicans want for review. Republicans said the IRS was obstructing their inquiry.

Congressional Democrats, for their part, accused Republicans of rehashing baseless accusations for political theater.

The IRS reviews the activities of non-profit organizations seeking tax exemption because U.S. law limits such groups' political involvement. Non-profits have increasingly been used as conduits for political spending, especially by conservatives, according to campaign finance watchdogs.

On June 13, the IRS informed lawmakers that it could not produce some of Lerner's emails from 2009 to 2011 because they were wiped out in a computer hard drive crash.

(Reporting by Kevin Drawbaugh; Editing by Lisa Shumaker)

[Image via Agence France-Presse]