Health and Human Services Secretary Kathleen Sebelius will not testify at a congressional hearing Thursday into breakdowns in the rollout of the federal Affordable Care Act, drawing more heat from House Republicans.

An HHS official confirmed Saturday that the secretary would not attend, citing a conflict in her schedule.

"We are in close communication with the committee and have expressed our desire to be responsive to their request,” the official said.

The hearing, before the House Energy and Commerce Committee, was scheduled this week to address glitches in the Obamacare website. Chairman Fred Upton, R-Mich., ripped Sebelius when initial reports indicated she would not attend.

"Secretary Sebelius had time for Jon Stewart, and we expect her to have time for Congress," he said in a statement, referring to her appearance last week on Comedy Central's "The Daily Show."

Saturday, Speaker of the House John Boehner joined the chorus blasting Sebelius in a post on Twitter:

HHS Secretary @Sebelius has time for galas & late night TV, but won’t testify about the #ObamaCare #trainwreck http://t.co/8vQWvJxx9N — Speaker John Boehner (@SpeakerBoehner) October 19, 2013

Since its launch, on Oct. 1, the site has been plagued by crashes as Americans to try log on and enroll for health insurance. The Obama administration has conceded that the launch has been rockier than it had hoped.