Sen. Tom CoburnTom Coburn'Path of least resistance' problematic for Congress Freedom Caucus saved Paul Ryan's job: GOP has promises to keep Don't be fooled: Carper and Norton don't fight for DC MORE (R-Okla.) accused any lawmakers promising not to touch Medicare of being liars.

"Any politicians that stands up and says, 'We're not going to touch your Medicare' is a liar," Coburn, who is famously blunt, said Thursday night in an interview with Oklahoma's News on 6.

His comments come as Democrats plan to hit Republicans' plans to change Medicare in their 2013 budget plan, which is expected to offer the same changes to the program Republicans proposed last year. Democrats successfully used the GOP budget to win a special House race in New York last May.

Democrats hope to capitalize on those cuts again and repeat attacks they made on House Budget Committee Chairman Paul RyanPaul RyanGOP leaders launch internal review into leak Opinion | Michael Steele: Gianforte better put his ‘big boy’ pants on Washington needs high-level science and technology expertise – now! MORE's (R-Wis.) plan, which would change Medicare into a voucher system for Americans who are now under the age of 55 when they turn 65.

In January, Ryan suggested the reforms in his plan were likely to reappear in the new plan.

"We haven't written it yet, but we're not backing off on the kinds of reforms we've advocated," Ryan said at the GOP's yearly issues conference in Baltimore. 

Coburn, along with Sen. Joe Lieberman (I-Conn.), proposed a plan last summer that would cut more than $640 billion from Medicare over the next 10 years, mostly by raising deductibles and other costs for beneficiaries.

—This story was last updated at 8:58 a.m.