HHS Secretary Kathleen Sebelius Resigning

— -- Health and Human Services Secretary Kathleen Sebelius will announce Friday she is stepping down, ABC News has confirmed.

The president will nominate Sylvia Burwell, director of the Office of Management and Budget, to replace her.

Sebelius approached President Obama about a month ago and asked to step down after the health care sign-up numbers were released, two senior administration officials and a confidante of Sebelius' told ABC News.

The White House always worried about finding someone to win confirmation at HHS, but Burwell was overwhelmingly confirmed as budget director with a vote of 96-0 about a year ago.

Earlier today Sebelius was on Capitol Hill to announce that 400,000 additional people have chosen insurance plans through the Obamacare exchanges as of this week, raising the total number of enrollees to approximately 7.5 million.

“As of this week, 400,000 additional Americans have signed up and we expect that number to continue to grow,” Sebelius said at a Senate Finance Committee hearing Thursday.

Last week, the administration announced 7.1 million people had enrolled as of April 1.

“From her work on Head Start, to expanding mental health coverage, to advancing cutting-edge health care research and, of course, her unwavering leadership in implementing the Affordable Care Act, Secretary Sebelius often calls her work here the most meaningful of her life,” an HHS official said in a statement. “As she closes this chapter, Secretary Sebelius is extremely thankful to President Obama and very proud of the historic accomplishments of this Administration.”

Sebelius, a former governor of Kansas, was among Obama's earliest supporters back in 2008. Her endorsement -- over Hillary Clinton -- came at a critical time in his first race for the White House.

But the president, while always fond of Sebelius, was furious at the rollout of the health care web site. He placed blame internally on her, aides said, among others.

Publicly, however, President Obama stood by her through the embarrassment.

“Kathleen Sebelius doesn’t write code. She wasn’t our IT person," Obama said in an interview with NBC News on Nov. 7.

Sebelius, herself, took responsibility for the mess during a series of hearings on Capitol Hill.

“Hold me accountable for the debacle. I’m responsible," she famously told the House Energy and Commerce Committee on Oct. 31, her first of many grillings on Capitol Hill.

Shortly after news of Sebelius’ resignation broke, Republican National Committee Chairman Reince Priebus took the opportunity to predict “that there are more problems on the way” for the president’s signature health care reform law.

“The next HHS Secretary will inherit a mess -- Americans facing rising costs, families losing their doctors, and an economy weighed down by intrusive regulations,” Priebus said in a statement. “No matter who is in charge of HHS, ObamaCare will continue to be a disaster and will continue to hurt hardworking Americans.”

ABC’s Arlette Saenz and Devin Dwyer contributed reporting.