WASHINGTON - Washington's top tax official was fired on Wednesday as President Barack Obama sought to stem a rising tide of criticism over the Internal Revenue Service's improper targeting of conservative groups for special scrutiny.With three congressional probes of the IRS looming and Republicans' calls for firings at the agency growing louder, Obama said he told Treasury Secretary Jack Lew to demand the resignation of Steven Miller, the acting IRS commissioner. Lew had done so, the president said."I'll do everything in my power to make sure nothing like this happens again by holding the responsible parties accountable, (and) by putting in place new checks and new safeguards," Obama told reporters in the White House's East Room.Obama's remarks came on a day in which he tried to regain the initiative amid a series of controversies that have threatened his second-term agenda. The Democratic president said new leadership was needed at the IRS to restore public confidence in the tax agency, whose reputation for political independence has taken a hit because of scandal."Americans are right to be angry about it, and I am angry about it," Obama said. "I will not tolerate this kind of behavior in any agency, but especially in the IRS, given the power that it has and the reach that it has into all of our lives."The IRS revelations have added to a sense of a White House under siege, and a president struggling to recover his political footing in the face of fast-moving events.Republicans continue to attack the administration's handling of militants' deadly attack last year on the US mission in Benghazi, Libya. On Monday, the Justice Department came under fire for seizing phone records of journalists from the Associated Press as part of a criminal probe into intelligence leaks.Obama spoke after meeting with senior Treasury officials on ways to quell the growing uproar after a government report found that poor management led to an "inappropriate" focus on claims by conservative groups for tax-exempt status.Obama, who had been accused by Republican critics of reacting too passively to the scandal, promised to work "hand in hand" with Congress to fix the IRS. But he acknowledged the realities of a politically divided Washington, and urged lawmakers to deal with the matter in a way that does not "smack of politics or partisan agendas."Republicans signaled, however, they were not satisfied with Miller's resignation and that they were determined to find out whether the White House encouraged, or knew about, the effort within the tax agency to single out conservative groups for more scrutiny.Several, including Representative Jim Jordan of Ohio, also complained they were misled by Miller and another top IRS official, Lois Lerner, over whether the agency had targeted conservative groups.Many Republican lawmakers are sympathetic with groups associated with the conservative Tea Party movement, which have complained since 2010 about overly aggressive IRS agents."More than two years after the problem began, and a year after the IRS told us there was no problem, the president is beginning to take action," Senate Republican Minority leader Mitch McConnell said."If the president is as concerned about this issue as he claims, he'll work openly and transparently with Congress to get to the bottom of the scandal - no stonewalling, no half-answers, no withholding of witnesses," McConnell said in an apparent reference to congressional Republicans' frustration with what they view as the administration's lack of cooperation in the Benghazi probe.