Chrysler's Jeep Liberty was recalled to fix a problem with the fuel tank.

Under fire for the allegedly slow pace of a recall affecting 1.6 million potentially fire-prone Jeeps, Fiat Chrysler officials insist they’ve already been stepping up the pace of the safety campaign, despite taking sharp criticism from the nation’s top automotive safety official last week.

Chrysler last year agreed to recall 1.56 million Jeeps that were linked to fiery rear-end collisions. The automaker initially balked, insisting the data did not justify targeting the Jeep models, but reversed course after it came under heavy pressure both from regulators and the media. The National Highway Traffic Safety Administration also agreed to reduce the number of vehicles that would be impacted by nearly half.

But more than a year after agreeing to the service action, the acting NHTSA Administrator, David Friedman, declared that the pace of the recall has been “woeful.” The agency – itself under fire for its handling of various safety issues this year – has been pressing Chrysler to pick up the pace.

Adding fuel to that fire: widespread news coverage of a flaming crash earlier this month that killed a young Michigan woman whose Jeep had not yet been repaired.

“Be assured Chrysler Group takes seriously its commitment to motor-vehicle safety,” Fiat Chrysler CEO Sergio Marchionne wrote in a letter to Friedman. “I feel compelled to deliver up-to-date information that should alleviate your concerns.”

The numbers suggest that things have not been moving all that fast, in fact. According to the maker, less than 10% of the vehicles covered by the recall have been fixed. That includes 112,829 Jeep Liberty SUVs produced between 2002 to 2007, or 13.2% of that model. And just 26,352, or 3.5% of the Jeep Grand Cherokees built from 1993 to 1998, have been repaired.

“These completion rates are not satisfactory to Chrysler,” acknowledged Chrysler’s safety czar Scott Kunselman, in a separate letter to NHTSA.

Part of the problem has been a shortage of the parts necessary to complete the repairs. Chrysler’s critics contend the SUVs are vulnerable to catching fire in rear-end collisions because of the placement of their gas tanks on the backside of the rear axle. In a controversial agreement with NHTSA, Chrysler’s fix involves placing a trailer hitch on the bumper to shift impact forces away from the gas tank.

(Lawmakers may bar registration of vehicles not repaired after recalls. For more, Click Here.)

But Chrysler insists it is not necessarily to blame for the slow pace. It says it has about 430,000 of the hitches in stock at dealerships around the country. If anything, it stresses that owners have not taken the recall seriously and haven’t been scheduling the necessary repairs.

That’s not necessarily a surprise. Even on the most well-run recall programs, NHTSA data show completion rates tend to run below 80%. And that can often take a year or more to achieve.

(Click Here for details about VW’s five-year investment plan.)

General Motors, which is trying to make repairs to 2.6 million vehicles due to a defective ignition switch recently said it has only fixed about half those vehicles because of slow consumer response. GM recently mailed out gift cards to 885,000 owners, promising to activate them once repairs are completed.

(To see more about a possible collaboration between Tesla and BMW, Click Here.)

Safety experts note that the older a vehicle is when targeted by recall the less likely it is to be serviced.

Some safety experts are calling on Congress to enact legislation that would bar owners from being able to re-register vehicles subject to recalls until they are repaired.