(Reuters) — The White House sought to limit the political damage from the troubled rollout of the government's health care website as Republicans increased pressure on Wednesday to delay parts of President Barack Obama's signature domestic policy.

Obama administration officials held a closed-door briefing for Democrats in the U.S. House of Representatives and planned a session with insurance company executives to explain steps they are taking to quickly resolve problems with Healthcare.gov.

Republican critics in Congress demanded a delay in a requirement of the health care law that uninsured Americans must purchase insurance or face a tax penalty. They also said they would intensify their investigations into the launch of the 2010 Affordable Care Act, known as "Obamacare."

"It is our job to hold them accountable, and when it comes to Obamacare clearly there is a lot to hold accountable," House of Representatives Speaker John Boehner told reporters.

The chair of the Democratic National Committee, Florida Representative Debbie Wasserman Schultz, told MSNBC that the administration should be willing to extend the open-enrollment period for people to sign up for insurance.

Online exchanges, or marketplaces, were designed to be the main way for millions of uninsured Americans to find out prices and buy health insurance plans required under the law, but the Oct. 1 debut has been marred by technical glitches that have kept many from signing on and making purchases. Those unable to sign up online can call a toll-free telephone number as an alternative.

The administration has so far declined to disclose the number of enrollments either online or by telephone.

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A prolonged delay in getting Healthcare.gov to work could jeopardize White House efforts to sign up as many as 7 million people in 2014, the first full year the law takes effect. The administration on Tuesday began what it has called a "tech surge," bringing in experts led by the administration's top economic aide Jeffrey Zients to analyze and fix the problems.

"I think what we learned is they're working hard to fix the problems," Representative Sander Levin of Michigan, senior Democrat on the House Ways and Means Committee, said after Wednesday's briefing.

House Democrats said there was no talk in Wednesday's briefing about whether the problems should lead to a delay of the individual requirement that every American have insurance or pay a tax penalty. The Congressional Budget Office has estimated a delay would reduce enrollment significantly.

Republicans, who oppose the health care law on the grounds that it is an unwarranted extension of the federal government, said the requirement should be delayed until the problems with the rollout are resolved.

"With so many unanswered questions and the problems arising around this rollout, it doesn't make any sense to impose this 1% mandate tax on the American people," House Republican Leader Eric Cantor told reporters on Wednesday.

Republicans, who have repeatedly tried to derail or delay the health care law since taking control of the House in the 2010 elections, also demanded more answers about the scope of the problems and how many people were signing up for insurance in the federal exchanges.

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Despite the announcement of the "tech surge," the administration has not provided details about what caused the problems, what is being done to fix them and who exactly is being brought in for the effort aside from Mr. Zients.

"This is not transparency, this is adding to the confusion and the fears surrounding the rollout of Obamacare," Rep. Cantor said.

Three committees in the Republican-controlled House have announced investigations of the law's rollout, which Rep. Cantor described as "nothing short of a debacle."

Health and Human Services Secretary Kathleen Sebelius has been the focal point of criticism for the problems and Republicans have demanded she step down, but so far the White House has rallied around her.

Denis McDonough, the White House chief of staff, told the New York Times on Tuesday that Secretary Sebelius "has the president's confidence. And she knows that."

In that same article, however, an unidentified White House aide was quoted as saying that Secretary Sebelius did not have the "access to the president that she really needs to make a difference" and that while "everybody thinks that she's the driving force" in implementing Obamacare, "unfortunately she's not."

Secretary Sebelius, who will testify to Congress next week, will attend the session with insurance company executives, including the chief executives of WellPoint Inc. and Humana Inc.

WellPoint raised its 2013 membership and profit forecasts in part to reflect coming market changes under the law, its chief executive, Joseph Swedish, said in a statement on Wednesday.

Republican Representative Tim Murphy, chairman of a House and Energy Committee panel that will hold a hearing on the problems on Thursday, said the government had "frittered away" more than $300 million in payments to contractors for a website that does not work.

"Either they didn't know what was going on in their own offices, or they were deliberately misleading us and the American people," Rep. Murphy said.