IRS official Lois Lerner insisted at a hearing on Wednesday that she had done nothing wrong, and invoked her Fifth Amendment rights against self-incrimination, the Hill reported.

"I have not done anything wrong. I have not broken any laws. I have not violated any IRS rules or regulations. I know some people will assume that I have done something wrong. I have not," she said before the House Oversight Committee. Lerner is the head of the IRS division overseeing tax-exempt groups that targeted conservative groups.

The House Oversight Chairman Darrell Issa dismissed her, but said she could be recalled. Many top panel members of the committee indicated that Lerner mislead them four times in 2012 about the IRS agency's targeting of Tea Party groups who sought tax-exempt status, months before the Treasury audit detailed the extra scutiny.

Neal Wolin, the deputy Treasury secretary also appeared before the panel on Wednesday, marking the first time a senior department has been called to testify in the probe.

Wolin testified that the findings in the inspector general's report were "absolutely unacceptable and inexcusable," however there was "no indication" the Treasury had any role in the targeting. The Treasury and White House officials underscored they were involved in discussions about how the agency would disclose the targeting, but had found out details about it after the fact.

"It's important in this context to make clear that Treasury's longstanding practice - spanning Republican and Democratic administrations- is not to involve itself in the details of the IRS's administration and enforcement of the nation's tax laws," Wolin said.

J. Russell George, the Treasury inspector general and the ousted IRS head Steven Miller acknowledged that mistakes were made in targeting conservative groups for special scrutiny when they applied for tax-exempt status but insisted that agents had not broken any laws, nor was there any attempt for covering anything up.

"As acting commissioner, I want to apologize on behalf of the Internal Revenue Service for the mistakes that we made and the poor service we provided," Miller told the committee. "The affected organizations and the American public deserve better."