Updated

Obama administration officials are beginning to respond to increasing pressure for a public explanation about the problem-plagued ObamaCare site, with the agency responsible vowing a "tech surge" to fix it and President Obama preparing to address the public on Monday.

The Department of Health and Human Services on Sunday posted a blog on its site with some preliminary statistics and an assurance to Americans that officials are “working around the clock” and “committed to doing better.”

Shortly before noon on Monday, the president will directly address the technical problems with the site that "he and his team find unacceptable," according to the White House.

The website has been mired in problems since going live Oct. 1, including crashes, slow response times and failing to allow customers to complete the online process by purchasing health insurance.

Also on Sunday, Illinois Democratic Sen. Dick Durbin said Health and Human Services Secretary Kathleen Sebelius would testify before Congress about the site, amid a growing call for her to accept requests to speak on Capitol Hill.

“Ultimately, Secretary Sebelius will testify,” Durbin, the Senate’s No. 2 Democrat, told “Fox News Sunday.”

The 918-word blog acknowledges the glitches have been “frustrating” for Americans and states roughly 500,000 applications for coverage have been submitted. It also states that healthcare.gov has had roughly 19 million unique visits, which “confirms that the American people are looking for quality, affordable health coverage, and want to find it online.”

Officials said in the post they have called in additional help to solve the problems.

The agency has said it will release information on how many people have purchased insurance but has not so far.

Insurance coverage under ObamaCare begins in January and those who fail to purchase insurance under the 2010 law will have to pay a tax penalty by March 31.

Sebelius and the entire administration have declined requests to testify on Capitol Hill.

The House Energy and Commerce Committee sent a letter directly to Sebelius last week asking her to testify Thursday on the matter.

Sebelius has yet to respond publicly, but reportedly plans to attend a gala the night before in Boston, which has fueled calls for resignation.

Florida Republican Sen. Marco Rubio said he’s “reluctant” to call for an immediate dismissal in such situations, but was critical of Sebelius for so far not agreeing to testify.

“Her refusal to testify and be transparent has undermined her credibility,” he told Fox News, adding her not testifying could lead to her resignation.

House investigators say they want to know whether officials involved in the website “didn’t know or didn’t disclose” problems, after repeatedly saying the site was “on track” to launch.

Missouri Republican Sen. Roy Blunt told Fox News that Sebelius’ position appears “unsustainable.”

“She cannot sustain it,” he said. “She’ll have to testify.”

Commerce committee Chairman Fred Upton began focusing on Secretary Sebelius after she went to Comedy Central’s “The Daily Show with Jon Stewart” last week to talk about the website.

“Secretary Sebelius had time for Jon Stewart, and we expect her to have time for Congress,” the Michigan Republican has repeatedly said.