Charles Dharapak/AP Photo

Amid a firestorm of criticism, President Obama today walked back his oft-repeated, unambiguous promise that "if you like your health plan, you can keep it."

With hundreds of thousands receiving cancellation notices from their providers, Republicans have slammed the president in recent days for misleading the American public. Today, Obama tweaked his original pledge.

"For the vast majority of people who have health insurance that works, you can keep it," he said in a speech in Boston.

Addressing what he called the "flurry in the news" about the cancellations, Obama urged Americans receiving these notices to shop for new coverage in the marketplace. "Most people are going to be able to get better, comprehensive health care plans for the same price or even cheaper than projected. You're going to get a better deal," he said.

The administration has said it should come as no surprise that the 5 percent of the population who purchase insurance on their own may be forced to switch plans because their coverage doesn't meet the new standards required under the Affordable Care Act.

In his starkest statement yet on the botched Obamacare rollout, the president said he is "not happy" with the technical problems plaguing the HealthCare.gov website and that he is taking it upon himself to fix it.

"There's no excuse for it. And I take full responsibility for making sure it gets fixed ASAP," he said.

The president's comments came just hours after Health and Human Services Secretary Kathleen Sebelius apologized to consumers and took full responsibility for what she described as the "debacle."

Speaking at historic Faneuil Hall where seven years ago his former rival Gov. Mitt Romney signed the state's health reform bill, Obama drew parallels between the two laws, noting that the Massachusetts rollout was also rocky.

"Health care reform in this state was a success. That doesn't mean it was perfect right away. There were early problems to solve. There were changes that had to be made," he said.

In Massachusetts, just 123 consumers signed up in the first month of enrollment. Today, 97 percent of Massachusetts residents have coverage.

The president used the Massachusetts experience to assure Americans that the problems with Obamacare will fade and that ultimately, consumers will benefit. "I'm confident these marketplaces will work because Massachusetts has shown that the model works," he said.