United States President Barack Obama has placed blame for the government shutdown squarely on House Republicans, saying that one faction of one party is holding the country hostage over ideological demands.
"This Republican shutdown didn't have to happen," Mr Obama said in remarks delivered at the White House Rose Garden.
"They shut down the government over an ideological crusade."
The president called on House Republicans to pass a resolution to fund the federal government and end the shutdown, which began at midnight when funding for much of the government ran out. The impact will depend how long the shutdown lasts, Mr Obama said, but inevitably it will hurt the economy.
"The longer this shutdown continues, the worse the effects will be," Mr Obama said.
"So once again I urge House Republicans to reopen the government."
Mr Obama spoke 13 hours after a partial shutdown of the federal government began. To underscore his point, the president used today's launch of the health insurance benefits House Republicans are seeking to defund, appearing with people who would benefit from the newly opened Affordable Care Act insurance marketplaces.
Mr Obama said Republicans have made depriving the uninsured of health care the centerpiece of the GOP agenda, and they were willing to shut down the government to do that.
"It's all about rolling back the Affordable Care Act," he said.
"This, more than anything else, seems to be what the Republican Party stands for."
After days of volleying legislation back and forth, the House and Senate failed to reach an agreement to continue funding the government. The fiscal year ended at midnight as the Democrat-controlled Senate held firm in its refusal to scale back the Affordable Care Act as part of a budget deal.
The process of shutting down an array of federal functions began Tuesday morning. Meantime, the Senate met briefly to reject a House-approved plan to convene a conference committee in an effort to forge a deal.
Mr Obama has said he is willing to discuss broader budget priorities and possible improvements to his signature health-care law but not under the threat of shutting down the government or defaulting on the country's obligations. The president has said he would reject any proposal that defunds or delays the law known as Obamacare.
The president called the law settled, saying, "It is here to stay."