(Reuters) - U.S. government safety regulators on Thursday told Chrysler Group LLC Chief Executive Sergio Marchionne that the company "have to get their act in gear" to speed up repairs of recalled Jeep SUVs that face a heightened fire risk.

David Friedman, deputy director of the National Highway Traffic Safety Administration, was asked by reporters if he was satisfied with Chrysler's performance in adding trailer hitches to affected Jeep SUVs to protect them in lower speed rear-end crashes.

"No. In fact, this morning I sent a letter to the chairman and CEO of Chrysler telling them they have to get their act in gear. They have to make sure they're getting those parts in the hands of consumers," Friedman said.

Chrysler is a unit of Fiat Chrysler Automobiles. Marchionne is chairman and CEO of Chrysler Group as well as CEO of Fiat Chrysler.

Earlier this month, Chrysler said it was intensifying its effort to reach owners of the 1.56 million older model recalled Jeep SUVs because so few were bringing them in to dealerships to have the trailer hitch assemblies installed.

Chrysler spokesman Eric Mayne on Thursday said the company has again stepped up its efforts to reach owners. Only about 137,000 of the 1.56 million owners have shown up at dealers to have trailer hitch assemblies installed, Mayne said.

As of Thursday, the Chrysler spokesman said, the company has 488,000 trailer hitch assemblies in stock.

Still, on Thursday, Friedman of NHTSA said, "They've told us they have nearly 400,000 parts and yet we're getting complaints from consumers saying the dealers are telling them there aren't any parts. Something is wrong there."

Chrysler is committed to the safety of drivers and passengers in its products, the spokesman said.

"Chrysler Group leads the industry with a recall-repair completion rate of nearly 80 percent. The industrywide average is approximately 70 percent," Mayne said.

After initially resisting NHTSA's requests for a recall, Chrysler in June 2013 announced the recall of 1.56 million Jeep SUVs. They were the model years 2002-2007 Jeep Liberty and 1993-1998 Grand Cherokee, with rear fuel tanks.

(Additional reporting by Bernie Woodall in Detroit; Editing by Grant McCool)