US President Barack Obama has said that "bad apple" insurance companies, not his signature healthcare law, are to blame for hundreds of thousands of people losing their coverage in the past few weeks.

As administration officials scrambled to fix technical problems on an online insurance marketplace that is central to the success of the Affordable Care Act, Mr Obama blamed private insurers for a separate problem that has had critics questioning his honesty.

The president had repeatedly promised that people who are happy with their health plans would not have to change coverage.

But the termination of individual policies has given opponents scope to criticize the programme.

The law, known popularly as Obamacare, requires insurers to offer a higher level of coverage.

Individuals who do not have policies that meet the new standards may see their policies cancelled at the end of the year, or may find that the monthly payments are beyond what they can afford.

Speaking in Boston, Mr Obama said those who are getting dropped will be able to find new options through the online insurance exchanges, or marketplaces, established under the 2010 law.

"Just shop around in the new marketplace," he said. "You're going to get a better deal."

He stressed that the law included a provision that allowed Americans to keep bare-bones plans created before the law was signed as long as insurers did not change or cancel them.

"Remember, before the Affordable Care Act, these bad-apple insurers had free rein every single year to limit the care that you received, or used minor pre-existing conditions to jack up your premiums, or bill you into bankruptcy," Mr Obama said.

The law is the most sweeping new social programme since the creation of Medicare and Medicaid in the 1960s.

It is intended to move the United States closer to the goal of universal care by using market-based mechanisms to deliver affordable insurance to less affluent families that have been priced out by decades of rising healthcare costs.

Technical woes, however, have prevented millions of Americans from exploring those options through the government's portal since it was unveiled.