WASHINGTON (AP) — The head of the Internal Revenue Service told House Republicans on Wednesday that it would take years to provide all the documents they have subpoenaed in their probe of how the agency handled tea party groups' applications for tax-exempt status.

The comments by IRS chief John Koskinen drew a frosty response from Republicans who run the House Government Oversight and Reform Committee, one of several congressional panels investigating the controversy. The panel's chairman, Rep. Darrell Issa, R-Calif., warned him he should comply with the request "or potentially be held in contempt" of Congress, a sometimes threatened but seldom-used authority.

Republicans indicated a willingness to speed the process by accepting certain documents first but showed no signs of backing off their demands for what Koskinen said would be millions of communications involving IRS and White House officials and others.

"We don't want the excuses anymore. Prioritize it. Put more lawyers on the job," said Rep. Jim Jordan, R-Ohio, a leading member of the committee. He added, "All means all."

"You've been more concerned with managing the political fallout than cooperating with Congress," Issa said.

Koskinen, who became IRS commissioner in December after the affair prompted a house-cleaning of top agency officials, said the service has provided more than 1.1 million pages of documents to congressional committees since their investigations began last spring. But he said it is taking time because by law, the IRS must remove sensitive personal information about taxpayers from any documents they give the Oversight panel.

"You're going to get a lot of emails" and other documents if the search isn't limited to relevant information, Koskinen told Issa. "You may want to have this investigation go on forever."

Koskinen later added that the GOP document request "is going to take years to produce."

Among the documents Issa's panel wants are all emails since 2009 to and from Lois Lerner, the former IRS official at the center of the controversy.

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Lerner has appeared twice before the Oversight committee but refused to answer questions, prompting Republicans to talk about voting to hold her in contempt of Congress. If Congress votes to approve a contempt charge, the matter is turned over to federal prosecutors, with conviction meaning a possible fine or prison term.

Lerner led the IRS division that reviewed applications for tax-exempt status and that improperly singled out conservative groups for close scrutiny during the 2010 and 2012 elections. Documents have shown that some liberal groups were also flagged.

So far, no evidence has been released showing that officials outside the IRS ordered the focus on conservative groups or were aware of it. Rep. Elijah Cummings of Maryland, the committee's top Democrat, said the panel is involved in a "partisan search for nonexistent connections to the White House."

By law, so-called social welfare organizations can qualify for tax-exempt status if they don't primarily engage in political activity, a determination that the IRS makes. The laws, regulations and definitions that govern the process are vague and sometimes contradictory.

The Obama administration has proposed rules narrowing the types of activities such groups could engage in and still qualify for tax exempt status.