WASHINGTON (REUTERS) - President Barack Obama said on Tuesday that some 4 million people had signed up for health insurance through exchanges provided by his signature healthcare law known as Obamacare.

Obama made the comments to a gathering put together by OrganiSing for Action, a political group formed from his 2012 campaign apparatus.

A full enrollment report for February will be released in mid-March, the lead Obamacare agency, the Centres for Medicare and Medicaid Services, said in a statement.

The figure given by Obama showed an increase of 700,000 from the 3.3 million people who had enrolled in private Affordable Care Act plans from Oct 1 to Feb 1. Enrollment has picked up momentum since the botched rollout of the HealthCare.gov website in October.

The deadline for enrolling for 2014 coverage is March 31, and the administration and allied groups are pushing to persuade more uninsured people in big cities to sign up.

The nonpartisan Congressional Budget Office has trimmed its enrollment forecast for 2014 to 6 million from its original projection of 7 million.

Vice President Joe Biden acknowledged last week that "we may not get to 7 million, we may get to 5 or 6, but that's a hell of a start".

Obama urged supporters on Tuesday to keep reaching out to people to get them signed up for health insurance coverage.

"We've got more work to do," he said, citing "a combination of an implacable opposition that has spent hundreds of millions of dollars, if not billions of dollars, spreading misinformation on this plan".

"You combine that with, let's face it, the website didn't work for the first month," he added Obamacare remains a target of attack by Republicans, who hope to use the programme's unpopularity with voters to craft a winning campaign message for the November election battle for control of Congress.