WASHINGTON -- Health and Human Services Secretary Kathleen Sebelius is resigning from the Obama administration after the rocky rollout of President Barack Obama's signature health care law, a White House official said Thursday.

Her resignation comes just one week after the end of the first enrollment period for the Obamacare law. While the opening weeks of the rollout were marred by website woes, the administration rebounded strongly by enrolling more than 7 million people in the new insurance marketplaces.

Sebelius' resignation following her five-year tenure in Obama's Cabinet comes as the White House seeks to rebound from the politically damaging launch of the health care law. But it could also set the stage for a contentious election-year confirmation hearing to replace her, as Republicans seek to make the health law the centerpiece of their efforts to retake the Senate in the November midterm contests.

The official said Obama was nominating Sylvia Mathews Burwell, the director of the Office of Management and Budget, to replace Sebelius. The official was not authorized to discuss Sebelius' resignation ahead of the formal announcement and requested anonymity.