In his first executive order, Donald Trump, the 45th president of the United States, told government agencies to scale back aspects of the Affordable Care Act - fulfilling his pledge to undo Barack Obama's signature healthcare law that made medical services accessible to millions of Americans.

The one-page order directs federal agencies to limit the "economic and regulatory burden" of the Affordable Care Act, as a prelude to a full repeal.

Trump built his campaign message around bold vows to, among other things, repeal the Affordable Care Act, which has come to be known as Obamacare. He called the programme a "disaster."

The act came into effect in 2010 and has helped about 20 million uninsured Americans get health coverage.

In broad language, the order says agencies must allow states greater flexibility in carrying out healthcare programmes and directs them to grant waivers, exemptions, and delays to provisions that would impose costs on states or individuals

Larry Levitt - the vice president of the Kaiser Family Foundation, a nonpartisan health-system analysis group - said it was a "sign that the Trump administration is looking to unwind the law in every way it can, administratively".

Levitt said broad exemptions from the law's coverage requirement could scare off insurers already on the fence about continuing to participate in 2018 and beyond.

Transcript: Donald Trump inauguration speech in full

The executive order may not have much impact for 2017, since government rules for this year have already been incorporated into contracts signed with insurance companies.

Leslie Dach, campaign director of the Protect Our Care Coalition, called the executive order "irresponsible".

"While President Trump may have promised a smooth transition, the executive order does the opposite - threatening disruption for health providers and patients," Dach said in a statement.