US President Barack Obama's health care law is on track to hit seven million sign-ups as a result of a deadline-day surge.
Two US officials spoke on condition of anonymity because they were not authorised to discuss the matter ahead of an official announcement.
Seven million sign-ups was the original target set by the Congressional Budget Office for subsidised private health insurance offered through new online markets.
That was scaled back to six million after the disastrous launch of HealthCare.gov last autumn.
The seven million-mark would beat expectations.
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The scramble to sign up under Obama's health care law at the end of a six-month enrolment window caused website glitches and long lines at on-the-spot enrolment centres.
But Republicans renewed a vow to repeal the law, which they say costs jobs, handcuffs small businesses and represents a government power grab in the private health care market.
More than two million people visited the Healthcare.gov website on Monday and another 840,000 called telephone enrolment centres, a White House official said.
"There has been a remarkable story since the dark days of October and November," said White House spokesman Jay Carney.
The health care law is Obama's signature domestic political achievement and the most sweeping social reform in decades in the United States.
Yet its passage and implementation ignited a partisan battle and highlighted deep ideological divisions cleaving the United States.
