Details added (the first version was published at 03:37)
The top US tax official resigned Wednesday after revelations that his agency, the Internal Revenue Service, had improperly scrutinized conservative groups applying for tax-exempt status, dpa reported.
Acting Commissioner of the IRS Steven Miller resigned at the request of Treasury Secretary Jacob Lew, President Barack Obama said.
Obama said he had reviewed an internal investigation of the IRS's actions and concluded that "the misconduct it uncovered is inexcusable."
Americans are right to be angry about it, he said, adding "I am angry about it. I will not tolerate this kind of behaviour 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," he said, speaking at the White House.
An inspection of IRS practices found that the federal tax collection agency used "inappropriate criteria" to target conservative political groups for extra scrutiny beginning in 2010.
Federal law allows non-profit groups to pursue public policy agendas but not to directly participate in election campaigns.
The federal tax agency last week admitted to targeting non-profit groups for extra scrutiny based on suspected associations with the so-called Tea Party, a conservative political movement that advocates smaller government and lower taxes. It first arose in 2009-10.
Miller had only served as chief of IRS since November. A George W Bush apointee, Douglas Shulman, led the agency prior to that.
Obama pledged to put in place new safeguards to prevent similar problems in the future and ordered Lew to implement the recommendations of the internal audit, including better explaining why groups are reviewed and better tracking of pending applications.
Speaker of the House John Boehner demanded earlier Wednesday that someone be fired in the scandal.
"The IRS has admitted to targeting conservatives," Boehner said. "Now, my question isn't about who's going to resign. My question is, who's going to jail over this scandal?"
The Obama administration has been reeling from one revelation after another in recent weeks, including disclosures that Obama's Justice Department snooped on telephone records of the Associated Press news service.
The administration has also come under renewed scrutiny for its handling of the terrorist attack that killed four Americans in Benghazi, Libya last year.
Earlier Wednesday, Obama aides released more than 100 pages of emails detailing the back and forth between the White House, State Department and CIA on the talking points about what happened in the attack.
The move comes after intense criticism last week when portions of the internal memos were leaked to the press, providing fodder for Republicans alleging the Obama administration attempted to downplay the event's terrorist origins.
Those reports showed extensive edits to talking points that were then used by UN Ambassador Susan Rice to discuss the attacks on television. She has been criticized for providing a faulty explanation of the attack that left four Americans, including the ambassador to Libya, dead.
On the secret seizure of AP journalists' phone records, Attorney General Eric Holder faced tough questions in Congress, but could offer no satisfying answers because he himself had been under investigation in the probe.
Under Department of Justice rules, only the attorney general can approve the subpoena of information from the media. Members of Congress also noted that media executives are supposed to be consulted before such steps are taken.
In the case of the AP, neither happened. Holder handed off responsibility for the subpoenas to a deputy, James Cole, recusing himself from the case because he had been questioned by investigators over the original leak.
But under questioning from Congress, he could not recall the date this happened, and he admitted there was no written record of the handoff.
The affair involved apparent leaks to the AP about a foiled terrorist plot in Yemen to bomb an airplane in May 2012. The story was widely reported in the US media, and John Brennan, the top White House counterterrorism official, reassured the public on May 8, 2012, that the bomb plot had not advanced sufficiently to be a public threat.
Outrage over the seizure of the AP phone records has provoked an outpouring of protests from US newspapers and industry organizations.
It has also sparked a renewal of efforts in Congress to pass a shield law that would protect journalists and their confidential sources.