ST. PAUL, Minn. — Gov. Mark Dayton and Republican legislative leaders abruptly abandoned closed-door mediation sessions on Friday, pitching their monthslong legal battle over the governor's veto of House and Senate budgets back to the courts.

The two sides have fighting since May over Dayton's decision to zero out the Legislature's $130 million operating budget, taking their dispute from a county courtroom to the state Supreme Court and into this week's court-ordered mediation. Dayton vetoed House and Senate funding in a bid for leverage to scale back costly tax breaks and undo other measures he signed into law as part of a new, $46 billion budget.

Two days of scheduled talks broke off early Friday afternoon, with each side casting blame on the other for the lack of progress and growing legal tabs as the case heads back to the Supreme Court with trust between the two government branches at an all-time low. Top Republicans claimed Dayton ended mediation and stormed off, while the Democratic governor accused lawmakers of obscuring how much money in budgetary reserves they had to continue running without a formal appropriation.

"I've never, ever, ever in my 40 years of government seen this kind of duplicity," Dayton said, acknowledging the saga had angered him. "This has just been a farce."

The two sides entered mediation Thursday morning with diametrically opposed views.

Citing the same reasons behind his late May veto, Dayton wanted lawmakers to scale down several costly tax breaks for wealthy estate owners and businesses and undo other provisions including a ban on issuing driver's licenses to immigrants living in the U.S. illegally. But Republicans showed little interest in renegotiating budget bills that Dayton signed into law, insisting that the governor's action was blatantly unconstitutional.

Instead, Senate Majority Leader Paul Gazelka said Republicans offered several, separate policy changes but wouldn't elaborate on what they entailed.

"We were looking for other avenues to give the governor a win and we could win as well," he said.

By lunchtime Friday, the two sides had made no progress and Dayton abruptly walked away. Court-appointed mediator Rick Solum said in a statement that their differences were "irreconcilable."

The mediation sessions were ordered by Minnesota's Supreme Court, which shied away from the legal battle with a nuanced order that deemed Dayton's use of the line-item veto constitutional while stressing that it cannot be used "to accomplish an unconstitutional result." It did not touch a lower court's ruling that was decidedly in the Legislature's favor.

Attorneys for both sides will inform the state Supreme Court that mediation has failed. With more than $245,000 in legal fees already on the books and lead attorneys that charge both the governor and Legislature at least $325 hourly, the case won't be cheap for Minnesota taxpayers.

Gazelka said he hopes the Supreme Court will take another look at the case and side in the Legislature's favor. If lawmakers' budget isn't restored, the majority leader and House Speaker Kurt Daudt said the Legislature may have to lay off some staff to stretch remaining budget reserves out until lawmakers return to the Capitol in February. Then they could vote to override Dayton's veto or simply pass a new budget.

"If we had to, we could limp through to next session," Gazelka said.

Dayton called those concerns overblown, noting that the Legislature had laid out plans to use more than $38 million in funding for an independent legislative staffing agency if necessary — more than enough to last into 2018.