(Reuters) -- Volkswagen, which is set to provide detailed plans to fix vehicles that do not comply with U.S. emissions standards, faced more pressure on Thursday from officials in Washington and California to buy back older diesel cars.

A California Air Resources Board spokesman said officials at the automaker are scheduled to meet Friday with CARB and the U.S. Environmental Protection Agency to present detailed proposals for recalling and fixing about 482,000 vehicles sold in the United States with diesel engines that emit more smog-forming pollutants than allowed by law.

California has set a Nov. 20 deadline for Volkswagen to come up with a plan to fix the diesel cars affected by its rigging of emissions tests. The carmaker said in September that around 11 million diesel powered cars were affected worldwide, including 482,000 in the United States.

"I am personally hopeful we will be able to announce something soon about the remedies ... and which we are discussing with the agencies in upcoming days," Michael Horn, head of Volkswagen's U.S. operations, said at the Los Angeles Auto Show on Wednesday.

The CARB spokesman also confirmed that the agency's head, Mary Nichols, told the German daily Handelsblatt that Volkswagen might have to buy back some of the older diesel models. "I think it is quite likely that they will end up buying back at least some portion of the fleet from the current owners," the paper quoted Nichols as saying in an interview to be published on Friday. Newer cars might get easy software fixes and medium generation ones might need software and hardware components to fix the issue, Nichols said, according to the paper. But older cars might have to be repurchased rather than fitted with new pollution control devices.

Separately, U.S. Senators Ed Markey of Massachusetts and Richard Blumenthal of Connecticut on Thursday released a letter calling on the automaker to buy back diesel vehicles that don't meet pollution standards. The lawmakers noted that Volkswagen had signaled it could buy back cars sold in Europe that have inaccurate carbon dioxide emissions ratings.

Volkswagen has admitted understating CO2 emissions, and thus understating fuel consumption, for about 800,000 vehicles sold in Europe, and possibly more.

“We additionally urge you to offer drivers the fair market value for these vehicles that was in place before VW’s illegal activity was made publicly known,” the lawmakers wrote.

VW spokeswoman Jeannine Ginivan declined to comment Thursday on the prospects of a U.S. buyback for some of the diesel vehicles. She said VW planned to meet with U.S. regulators on Friday to lay out plans and discuss remedies to fix the 482,000 vehicles.

(Reporting By Rory Carroll and Kirsti Knolle; editing by Joe White and David Gregorio)