Washington: Republican criticism rained down on the second anniversary of President Barack Obama's health care reform, with Mitt Romney blasting the law as an "unfolding disaster for the American economy."

As conservatives bashed "Obamacare" as an assault on economic liberties that would saddle Americans with unprecedented financial burden, the administration marked the anniversary of the president's signature legislative achievement in muted fashion, with no ceremony at the White House.

Romney's rival in the Republican presidential race, former House speaker Newt Gingrich, savaged the two-year-old law as "the most dangerous legislation in generations," while Senate Minority Leader Mitch McConnell slammed it is "a metaphor for all of the excesses of this administration."

In a piece for USA, Romney, frontrunner for the Republican nomination in the battle to see who will challenge Obama in November, said it was "past time to abolish the program, root and branch."

And while he noted that the US Supreme Court was set to hear arguments about the landmark law next week, he wrote that, regardless of how the justices rule, "the case against Obamacare extends far beyond questions about its constitutionality.

"President Obama's program is an unfolding disaster for the American economy, a budget busting entitlement, and a dramatic new federal intrusion into our lives," Romney wrote.

The Affordable Care Act, passed after a bitter struggle against blanket Republican opposition in 2010, granted 30 million Americans health insurance for the first time, bringing universal coverage closer than ever before.

Romney instituted a similar program for Massachusetts while he was governor of the left leaning state, and in 2009 he wrote an op-ed in the same newspaper encouraging Obama to use the Massachusetts model as a basis for his national health program.

But yesterday Romney said he is vehemently opposed to a one-size-fits-all health care plan for the entire nation.

"What we need is a free market, federalist approach to making quality, affordable health insurance available to every American," he wrote in USA Today. "Each state should be allowed to pursue its own solution in this regard, instead of being dictated to by Washington."

He repeated the message at a campaign stop in Louisiana, which holds its Republican primary on Saturday, saying if elected he would "return to the states" the authority and responsibility to care for the uninsured.