The head of the scandal-plagued IRS apologized to Congress Friday for \"foolish mistakes\" made by the federal tax agency in targeting conservative groups but insisted the action was not politically motivated. Amid swirling controversy buffeting the US capital, lawmakers hammered Steven Miller, who offered his resignation as demanded by President Barack Obama, over abuse at the agency that Democrats and Republicans alike criticized as outrageous and unacceptable. The Internal Revenue Service acknowledged a week ago that, beginning in 2010, a team of employees inappropriately screened conservative groups, including those with \"Tea Party\" and \"Patriots\" in their names, as they applied for non-profit status. \"I want to apologize on behalf of the Internal Revenue Service for the mistakes that we\'ve made and the poor service we provided,\" Miller told a tense hearing at the House Ways and Means Committee. While he stressed that \"even the perception of partisanship has no place at the IRS,\" Miller said \"I do not believe that partisanship motivated the people who engaged in the practices described\" in an internal report on the abuse.\"Foolish mistakes were made by people trying to be more efficient in their workload selection.\" Miller faced questioning from Republican committee chairman Dave Camp, who was incredulous that despite a two-year congressional probe, the IRS never told lawmakers that top officials in the IRS, including Miller, knew about the abuse back in May 2012. \"In fact, we were repeatedly told no such targeting was happening,\" Camp told Miller. \"That isn\'t being misleading, that is lying.\" Camp demanded that Miller tell Congress \"who started the targeting, who knew, when did they know, and how high did it go?\" Obama said Thursday he had no prior knowledge of the abuse, and Miller told the hearing he \"absolutely\" did not contact the White House when he first learned of the burdensome scrutiny on the conservative groups last May. Lawmakers like Republican Kevin Brady demanded to know exactly who was responsible for the wrongdoing, but Miller was not forthcoming. \"I don\'t have names for you, Mr. Brady.\" The fury was bipartisan, as the committee\'s top Democrat, Sander Levin, called for the resignation of Lois Lerner, the senior IRS official who acknowledged the wrongdoing a week ago, just days after telling a congressional committee nothing of the abuse. \"We\'re all outraged, we\'re all upset about this,\" said Democrat Joseph Crowley. Veteran Democrat Charles Rangel seethed at Miller, saying the IRS\'s reputation, as well as that of the president and the administration, was on the line. \"People are losing confidence in our government and I hope you feel the same sense to find out what... happened.\"