The failure of the U.S. and South Korea to meet a deadline Thursday for a revised free-trade deal prompted warnings from two key U.S. congressmen, who said more must be done to open up the Asian country's auto market.

A leading U.S. business group, meanwhile, said it would "pull out all the stops" to lobby for quick passage of a deal.

"Further negotiations will succeed only if South Korea adopts concrete steps to open its market to U.S. exports," Michigan Reps. Sandy Levin and Dave Camp said in a joint statement after the countries said they would extend talks beyond Thursday. "While there are other unresolved issues, nowhere is this more evident than in the dangerously lopsided trade in automotive vehicles."

Levin is the Democratic chairman of the House Ways and Means Committee, which has jurisdiction over free-trade deals. Camp is the panel's ranking Republican and in line to become chairman when the new Congress takes over in January. They are also key allies of the auto industry.

The U.S. Chamber of Commerce said in a statement it was "disappointed" at Thursday's outcome but believes progress has been made and differences "narrowed."

"We urge both presidents to direct their ministers and staff to resolve remaining details with the greatest possible speed and urgency," the Chamber said. "Time is of the essence. American jobs are on the line."

The Chamber said that with the imminent implementation of a trade deal between South Korea and the European Union, the U.S. could lose 340,000 jobs without its own deal in place.

"The Chamber is ready to pull out all the stops to explain the benefits of this agreement to the American people and help move the pact through Congress," the statement said. "The sooner we get this deal done, the sooner it will start creating new American jobs."

Lori Wallach, a trade expert at watchdog group Public Citizen, a skeptic of the original U.S.-South Korea pact proposed during the George W. Bush administration, called on President Barack Obama to ensure the deal wouldn't lead more U.S. companies to move operations overseas, costing American jobs.

"The political liability of an Obama flip-flop on his election trade reform commitments by pushing Bush's NAFTA-style Korea deal without delivered the significant changes he promised, including to the job-offshoring investment rules, cannot be overstated," Wallach said in a statement.

-By Josh Mitchell, Dow Jones Newswires; 202-862-6637; joshua.mitchell@dowjones.com