US President Donald Trump has threatened to end government payments to health insurers unless politicians repeal and replace the "imploding" Obamacare law.

Mr Trump took to Twitter this morning in apparent frustration over Friday's failure by the Senate Republican majority to pass a bill repealing parts of the Affordable Care Act.

"If a new HealthCare Bill is not approved quickly, BAILOUTS for Insurance Companies and BAILOUTS for Members of Congress will end very soon!" he wrote.

The first part of Mr Trump's tweet appeared to be referring to the approximately $US8 billion in cost-sharing reduction subsidies paid by the Government to insurers to lower the price of health coverage for low-income individuals.

The second part of the tweet appeared to be a threat to end the employer contribution for members of Congress and their staff, who were moved from the normal federal employee healthcare benefits program onto the Obamacare insurance exchanges as part of the 2010 healthcare law.

Mr Trump urged Senate Republicans to try again on a healthcare vote.

The Senate is in session for another week before it is scheduled to begin an August recess.

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Many insurers have been waiting for an answer from Mr Trump on whether they will continue to fund the annual government subsidies.

Without assurances, many insurers plan to raise rates an additional 20 per cent by an August 16 deadline for premium prices.

The Senate's Democratic leader, Chuck Schumer of New York, said health care risked becoming even more expensive.

"If the President refuses to make the cost sharing reduction payments, every expert agrees that premiums will go up and health care will be more expensive for millions of Americans," Mr Schumer said.

"The President ought to stop playing politics with people's lives and health care, start leading and finally begin acting presidential."

Mr Trump has only guaranteed the insurance payments through this month, which ends on Monday (local time).

What is Obamacare? Affordable Care Act passed by Congress in 2010

Affordable Care Act passed by Congress in 2010 Promised to help tens of millions of uninsured Americans get health coverage

Promised to help tens of millions of uninsured Americans get health coverage Under the plan, people can buy cheap insurance on healthcare.gov

Under the plan, people can buy cheap insurance on healthcare.gov Most coverage costs less than $US100 per month

Most coverage costs less than $US100 per month Policies vary according to person's income, location, family size and level of coverage desired

Policies vary according to person's income, location, family size and level of coverage desired More than 10 million people now have medical cover under the laws

More than 10 million people now have medical cover under the laws Number of uninsured adults reduced by 26 per cent

He has previously said the Obamacare law would stop immediately whenever those payments stop.

After the bill failed on Friday, Senate Majority Leader Mitch McConnell said he would move to other legislative business in the upcoming week.

But some congressional Republicans are still trying to find a way forward on healthcare reform.

Lindsey Graham said late on Friday that he and two other Republican senators, Dean Heller and Bill Cassidy, met with Mr Trump after the defeat to discuss Senator Graham's proposal to take tax money raised by Obamacare and send it back to the states in the form of healthcare block grants.

Senator Graham said the move would end Democrats' drive for a national single-payer healthcare system by putting states in charge.

"President Trump was optimistic about the Graham-Cassidy-Heller proposal," he added.

"I will continue to work with President Trump and his team to move the idea forward."

Sorry, this video has expired 'The motion is not agreed to': Obamacare amendment fails in US Senate

AP/Reuters