Billionaire brothers who bankroll Republican causes have distanced themselves from the GOP's high-risk shutdown strategy

Charles and David Koch, the reticent billionaires who bankroll Republican causes and candidates, have distanced themselves from their favoured party's financial brinkmanship as corporate America reacts with growing horror to the imminent prospect of a US debt default.

Money from Koch sources has supported many conservatives in Congress who have led the charge to shut down the government and breach an imminent debt limit if Barack Obama does not abandon his healthcare reforms.

But the brothers' privately held chemical conglomerate, Koch Industries, issued a rare public statement on Wednesday to deny allegations that the pair supported the high-risk strategy, and urged Congress to focus instead on balancing the budget.

“Koch believes that Obamacare will increase deficits, lead to an overall lowering of the standard of healthcare in America, and raise taxes,” spokesman Philip Ellender said in a letter to US senators. “However, Koch has not taken a position on the legislative tactic of tieing the continuing resolution to defunding Obamacare – nor have we lobbied on legislative provisions defunding Obamacare.”

The letter appears to have been prompted by mentions of the company's role during a debate in the Senate. Harry Reid, the Democratic majority leader, blamed Republicans for favouring the interests of their biggest donor over the American people, citing a New York Times report on the roots of the shutdown crisis.

“According to the news article, a former attorney general of the United States, Ed Meese, and the Koch brothers, have been raising and spending hundreds of millions of dollars to get us where we are right now,” said Reid. “We are satisfying the Koch brothers and Ed Meese, but millions of people in America are suffering.”

Koch presented its response as a matter of correcting the record. “A great deal of what you read and hear about Koch Industries is erroneous or misleading,” said the letter.

The company's intervention comes as Wall Street leaders and corporate America are becoming increasingly vocal about the dangers of triggering a devastating credit default if the US debt limit is not raised before next Thursday's deadline.

On Tuesday, the price of short-term government debt fell by a half, pushing up the cost of borrowing by the same amount, as investors took fright at the prospect that the US will miss interest payments next month.

Finance leaders have for some time been wary of the increasingly radical Republican tactics , which a Wall Street Journal editorial described as “kamikaze”, but the growing anxiety among mainstream corporate America and party donors such as Koch may prove to be what forces the party leadership to rethink.

The Koch letter suggested it continued to support long-term Republican objectives but would favour less confrontational methods to secure them. “We believe that Congress should – at a minimum – keep to sequester-level spending guidelines, and develop a plan for more significant and widespread spending reductions in the future,” it said.

“Congress should focus on these efforts: balancing the budget, tightening and cutting government spending, curbing cronyism, and eliminating market-distorting subsidies and mandates.”