WASHINGTON (Reuters) - Some 11.4 million Americans enrolled in private health insurance through Obamacare during the open enrollment period, the White House said in a tweet on Tuesday.

"The Affordable Care Act, aka Obamacare, is working. It's working better than we anticipated, certainly working a lot better than many of the critics talked about early on," President Barack Obama said in a video linked to the White House tweet.

Administration officials have said they expected 9.1 million people to be enrolled in coverage and up to date on insurance payments by the end of the year. The nonpartisan Congressional Budget Office had predicted 12 million enrollees for 2015.

Last April, the Obama administration announced that more than 8 million people had selected plans for 2014. But by the end of last year, only 6.7 million were still enrolled.

Obamacare's open enrollment period for 2015 began on Nov. 15 and closed on Sunday.

The White House said there had been a surge of applications in the last nine days of enrollment, particularly on Sunday.

"Sunday, February 15 was the biggest enrollment day ever: more new consumers signed up for health coverage than on any day this open enrollment period or the last," the White House said in a statement.

The U.S. Health and Human Services Department said on Saturday that a technical problem had prevented some consumers from enrolling but that the issue, involving income verification, was fixed late on Saturday.

The department said on Saturday that anyone who had been unable to submit an application because income could not be verified due to that problem or any other technical issue would receive an extension for enrollment.

Plans for Obamacare, formally known as the Affordable Care Act, are sold on HealthCare.gov for 37 states. The other 13 states plus Washington, D.C., run their own websites.

The Obama administration said last week that 2015 Obamacare subsidies were averaging $268 a month for people in the 37 states who had qualified for federal assistance.