President Barack Obama says the acting commissioner of the Internal Revenue Service, Steven Miller, has submitted his resignation in the aftermath of an investigation that found the agency improperly targeted conservative groups.

President Barack Obama (Olivier Douliery - Pool/Getty Images)

Obama says Treasury Secretary Jacob Lew requested Miller's resignation.

Obama says the IRS conduct was inexcusable, and he's angry about it. He also insists that safeguards be put in place to prevent reoccurrence of improper actions.

Obama has been under pressure to act in the aftermath of acknowledgement by top IRS officials that conservative groups were improperly singled out. An investigation by a Treasury inspector general found that the IRS used inappropriate criteria that identified for review tea party and other conservative groups that were seeking tax exempt status.

Obama spoke from the White House East Room after conferring with Lew and his top deputy.

The president said he would answer questions about the matter at a news conference today. Watch live video of the conference here.

Holder: Lawbreakers will be held accountable

Attorney General Eric Holder testifies during a hearing before the House Judiciary Committee (Alex Wong/Getty Images)

When it comes to the IRS targeting of conservative groups, Attorney General Eric Holder vows, "Anybody who has broken the law will be held accountable."

But he told lawmakers today that it will take time to determine if there was any criminal wrongdoing.

Holder says the criminal investigation will cover possible civil rights violations, false statements, and potential violations of the federal ban on some partisan political activities by federal employees.

He told the House Judiciary Committee that the investigation won't be about parties or about ideologies.

Three congressional committees are investigating the IRS for singling out tea party and other conservative groups during the 2010 and 2012 elections.

A report yesterday from a Treasury inspector general said ineffective management at the IRS allowed agents to improperly target tea party groups for more than 18 months.

Religious groups say they were scrutinized by IRS

Two conservative religious groups are saying they have faced unusual scrutiny from the Internal Revenue Service.

The son of Rev. Billy Graham and leaders of the Jewish organization Z Street say they believe the IRS targeted them because they advocated for conservative causes.

In a letter Tuesday to President Barack Obama, the Rev. Franklin Graham says charities built by his father, Billy Graham, may have received extra scrutiny from the IRS because they advocated against gay marriage while the elder Graham appeared in ads urging support for candidates who oppose abortion.

Members of Z Street filed a lawsuit in 2010 after the group's application for tax-exempt status stalled. The group's president, Lori Lowenthal Marcus, told Fox News that she believes her organization was targeted because of its views on Israel.