A bill to repeal the US health care law known as Obamacare has been announced by Republicans, which if passed is likely to leave more Americans uninsured.

The move to scale back the government’s role in helping people afford health insurance has long been a goal of party members including President Donald Trump.

House committees will start voting tomorrow on the 123-page bill, which replaces the Affordable Care Act, signed in 2010 by former President Barack Obama.

For years, Republicans have vowed to repeal the law – Mr Obama’s signature domestic policy achievement – but failed to agree on an alternative.

Despite a boost from the backing of Mr Trump’s administration, the success of the new legislation is not guaranteed as divisions remain and fierce battles on the issue could be seen in Congress.

Obamacare is popular in many states, including some controlled by Republicans. Public support for the policy is at the highest level since its introduction, with 54 per cent approval, according to the Pew Research Centre.

The Act has brought health insurance coverage to about 20 million previously uninsured Americans, although premium increases have angered some.

Donald Trump shifts his position on Obamacare during CBS 60 minutes interview

Critics of the law condemn it as government overreach, and Mr Trump has called it a “disaster”, although it remains unclear where the President stands on the details of the new bill.

“Today marks an important step toward restoring healthcare choices and affordability back to the American people,” the White House said in a statement.

The package replaces income-based subsidies received by millions of Americans through the Affordable Care Act with age-based tax credits, and abolishes fines on those who remain uninsured.

The tax credits will be phased out for higher-earning people but could prove insufficient for people on low incomes, leaving them unable to pay for health insurance.

The bill would continue Mr Obama's expansion of social health care programme Medicaid to additional low-earning Americans until 2020. Beginning then, states adding Medicaid recipients would no longer receive the additional federal funds the law has provided.

The Republicans plan to overhaul the entire federal-state Medicaid program, changing its open-ended federal financing to a limit based on enrolment and costs in each state, a move likely to cause funding cuts.

In a risky political gamble, the plan is expected to cover fewer people than are insured under Obama's overhaul, including many residents of states won by Mr Trump in November's election.

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House Speaker Paul Ryan said the bill would “drive down costs, encourage competition, and give every American access to quality, affordable health insurance.”

Republicans said they don't have official coverage estimates yet, but aides from both parties and nonpartisan analysts have said they expect those numbers to be lower.

Democratic House Minority Leader Nancy Pelosi said: “Republicans have decided that affordable health care should be the privilege of the wealthy, not the right of every family in America.”

Just before the plan was unveiled, four moderate Senate Republicans jointly expressed concern that an earlier draft would not adequately protect those who got coverage under Medicaid, raising doubts about the legislation's future in the Senate.

Conservative Republicans have also complained that the measure is too timid in repealing Mr Obama's law.

“It still looks like Obamacare-lite to me,” said Senator Rand Paul, one of three Senate conservatives who have criticised the Republican bill. “It's going to have to be better.”

Thirty-one states and the District of Columbia expanded Medicaid coverage to 11 million people and accepted beefed-up federal spending for the program during Mr Obama’s presidency.

Around half those states have Republican governors, who are largely reluctant to see that spending curtailed.

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In another feature that could alienate moderate Republicans, the measure would block for one year federal payments to Planned Parenthood, long opposed by many in the party because it provides abortions.

The bill also bars people from receiving tax credits to help pay premiums for plans that provide abortions.

Popular consumer protections in Mr Obama's law would be retained, including insurance safeguards for people with pre-existing medical problems and parents' ability to keep adult children on their insurance until age 26.

The overall cost of the Republican plan, a key issue in a time of high federal deficits, was not yet known, Republican aides said. Two House committees will next review the plan.

Craig Garthwaite of Northwestern University said the proposed tax credits, which would range from $2,000 to $4,000, were “frankly not enough for a low-income person to afford insurance.”

Republicans said the legislation would give Americans the flexibility to make their own healthcare choices, free of Obamacare's mandate that people buy health insurance and the law's taxes, including a surtax on investment income earned by upper-income Americans.

“Our legislation transfers power from Washington back to the American people,” House Ways and Means Chairman Kevin Brady said in a statement.