Republicans responded to news of Health and Human Services Secretary Kathleen Sebelius' resignation from the Obama administration on Thursday with fresh calls to repeal the president's health care law.

Sebelius leaves the administration after the tumultuous launch of the Affordable Care Act exchanges last fall. Despite calls for her ouster from Republicans at the time, she stayed on until the enrollment period ended at the end of March.

A White House official said President Obama will formally make the announcement on Friday, and nominate White House budget office director Sylvia Matthews Burwell to replace the outgoing secretary. The Senate would have to confirm Burwell to the position.

Republicans quickly made clear that Sebelius' departure will not temper their criticisms of ObamaCare.

"Virtually everyone who has come into contact with this law has had new reason to worry about what it means for the government to control their health care," Senate Minority Leader Mitch McConnell, R-Ky., said in a statement. "Secretary Sebelius may be leaving, but the problems with this law and the impact it’s having on our constituents aren’t. ObamaCare has to go, too."

Senate Finance Committee Ranking Member Orrin Hatch said Sebelius "had one of the toughest jobs in Washington" because she had to implement the law, which he said is "flawed" and continues to fall short.

"While we haven’t always agreed, Secretary Sebelius did the best she could during the tumultuous and volatile rollout of the law," Hatch, R-Utah, said in a statement.

Republican National Committee Chairman Reince Priebus said Sebelius' resignation will not fix problems with ObamaCare.

"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."

The administration touted the surge in enrollment in the last few weeks, with Sebelius saying Thursday that 7.5 million American have now signed up for coverage under the law.

But the technical difficulties surrounding the launch, as well as ongoing concerns about the implementation of the law, hung over her. She leaves just one week after the enrollment period ended, and as a tough midterm election cycle expected to focus heavily on ObamaCare begins.

House Minority Leader Nancy Pelosi praised Sebelius' leadership during the rollout, saying she had "been forceful, effective, and essential."

"Her legacy will be found in the 7.5 million Americans signed up on the marketplaces so far, the 3.1 million people covered on their parents' plans, and the millions more gaining coverage through the expansion of Medicaid," Pelosi, D-Calif., said.

The White House official said Sebelius notified Obama of her decision to leave in early March.

"At that time, Secretary Sebelius told the president that she felt confident in the trajectory for enrollment and implementation of the Affordable Care Act, and that she believed that once open enrollment ended it would be the right time to transition the department to new leadership," the official said, adding the president "is deeply grateful for her service."

West Virginia Democratic Sen. Joe Manchin praised the nomination of Burwell, a fellow West Virginia native, in a statement Thursday.

"I am confident that her leadership will ensure that we enact commonsense fixes to the Affordable Care Act to help improve the lives of millions of Americans," Manchin said.

Rep. Steve Daines, R-Mont., who is running to fill the seat vacated by Democratic Sen. Max Baucus, said in a statement that Sebelius' resignation "has been a long time coming—but it’s too little, too late."

"While Secretary Sebelius' resignation is a good start, it's not enough—we need to repeal ObamaCare before further harm comes to Montana families, and replace it with Montana-driven reforms that put the patient and their doctor—not government bureaucrats—in charge of health care decisions," Daines said.

Sebelius, having served five years with the president, was among the longest-serving Cabinet secretaries in the administration.

But Sebelius' relationship with the White House frayed during last fall's rollout of the insurance exchanges that are at the center of the sweeping overhaul. The president and his top advisers said they were frustrated by what they considered to be a lack of information from HHS over the extent of the website troubles.

The White House sent management expert Jeffrey Zients to oversee a rescue operation that turned things around by the end of November.

The Associated Press contributed to this report.