(CNN) - Senate Majority Leader Harry Reid fired away Wednesday at political ads hitting Obamacare funded by the billionaire Koch brothers that he says are all "untrue."
Reid later eased off some of his comments, but continued to pile on criticism of Americans for Prosperity.
That group, backed by conservatives Charles and David Koch, has flooded airwaves with ads attacking vulnerable Democratic senators up for reelection and Senate candidates for their support of Obamacare.
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In opening remarks on the Senate floor Wednesday, Reid said "there's plenty of horror stories being told" despite 4 million enrollees in the health care program.
"All of them are untrue, but they're being told all over America," he said, calling the AFP ads that characterize sky-rocketing premiums, dropped insurance plans and other negative effects of the law "absolutely false."
Reid's comments drew swift outrage from Republicans who responded on the Senate floor and continued to highlight problems with the law.
The Nevada Democrat later "walked back" the comments but continued to accuse the Koch brothers of "trying to buy America" with false stories of Obamacare.
"I can't say that every one of the Koch brother's ads are a lie," he said, but insisted, "a vast, vast majority of them are."
"What is going on with these two brothers who made billions of dollars last year in an attempt to buy our democracy is dishonest, deceptive, false and unfair. Just because you have huge amounts of money, you should not be able to run these false, misleading ads by the hundreds of millions of dollars."
The Koch-backed group has spent more than any other outside political group this cycle.
AFP says it has spent more than $25 million in ads attacking the health care law since October. The group has unleashed rounds of commercials that hammer lawmakers for supporting Obamacare.
It has zeroed-in on Democrats like Sens. Kay Hagan of North Carolina, Mary Landrieu of Louisiana and Jeanne Shaheen of New Hampshire, who are facing tough reelection challenges.
AFP responded to Reid's comments, saying they were evidence Democrats are trying to move attention away from the short-comings of Obamacare.
"Instead of admitting that the health care law is a bad deal for Americans, Senator Reid has chosen to attack the brave men and women who are sharing their personal stories about Obamacare," AFP spokesman Levi Russell said in a statement.
- CNN Political Editor Paul Steinhauser contributed to this report.