House Speaker John Boehner abruptly broke off talks with President Barack Obama Friday night on a deal to cut federal spending and avert a threatened government default, sending compromise efforts into an instant crisis.

In secretive endgame negotiations, President Barack Obama and House Republican leaders reached anew on Thursday for an elusive "grand bargain" deal to cut deficits by $4 trillion or more and prevent a threatened Aug. 2 government default, officials said.

In a blunt challenge to Republicans in Congress, President Barack Obama insisted Wednesday that elimination of selected tax breaks for oil companies and the super-wealthy must be included in any deficit reduction plan.

Two Senate rebels jumped into Congress' cut-the-deficit competition on Tuesday, proposing to raise the age of Medicare eligibility to 67 and increase monthly premiums for millions of current beneficiaries.

Republicans pulled out of debt-reduction talks led by Vice President Joe Biden with a flourish on Thursday, blaming Democrats for demanding tax increases as part of a deal rather than accepting more than $1 trillion in cuts to Medicare and other government programs.

To reduce government red ink, Republicans are willing to raise government revenues, but not increase taxes. Congressional Democrats would accept reductions in Medicare spending, yet no cuts in benefits.

Jubilant Democrats demanded Republicans abandon their sweeping plans to remake Medicare on Wednesday after casting a House race in upstate New York as a referendum on the popular program and emerging victorious.

Little more than a month after they backed sweeping changes to Medicare, Republicans are on the political defensive, losing a House seat long in their possession and exhibiting significant internal strains for the first time since last fall's election gains.