Three years after Fiat Chrysler and federal regulators agreed to a recall to fix more than 1.56 million Jeep SUVs that could catch fire in the event of a rear-end crash, safety advocates are calling on the government to reopen an investigation into the alleged defect, claiming that an additional 11 fatalities, possibly more, have occurred since that recall was initiated.

From model years 1993 through 2007, some Jeep Grand Cherokee and Liberty SUVs were made with plastic gas tanks mounted behind the rear axle. In a collision, these tanks could rupture possibly catching fire.

A 2013 recall fix was supposed to minimize the danger of a gas tank fire, but the Center for Auto Safety says that since the recall process began, 11 people have died from fires in the recalled Jeeps.

In a letter [PDF] to Transportation Secretary Anthony Foxx and the National Highway Traffic Safety Administration, CAS calls on the government to reopen its investigation into the Jeep defect.

NHTSA and Chrysler have been involved in a bit of back-and-forth with regard to the Jeep vehicles with rear-mounted fuel tanks that sit too low and put the vehicle at risk of catching fire if involved in a rear-end explosion.

Chrysler has maintained that the millions of Jeeps do not have a safety defect. However, at the time, safety documents showed that the issue has resulted in nearly 75 deaths.

During the summer of 2013, the car manufacturer and National Highway Traffic Safety Administration agreed to a remedy for the issue that involved equipping vehicles with a trailer hitch that could reduce the risk of fires.

NHTSA tested the hitch fix and determined that “the risk of fuel tank ruptures and fires in lower to medium-speed rear-end crashes will be successfully reduced by the remedy.” However, the agency did not test what would happen in collisions at speeds greater than 43 mph.

In the letter to Secretary Foxx, CAS contends that “more people will die from fire in recalled Chrysler Jeeps because the recall remedy negotiated behind closed doors … is totally ineffective.”

The group calls on the government to “obtain a remedy that saves lives versus the fire deaths that will continue to occur if Fiat Chrysler is left alone.”

NHTSA spokesperson Gordon Trowbridge told the Associated Press on Friday, that he couldn’t comment on the letter, saying he had just received a copy.

Last spring, NHTSA chief Mark Rosekind announced that the agency would consider reopening the investigation, noting that he’d created a group of regulators at the agency that will focus on the Jeep issue following additional deaths and a jury verdict that found Chrysler acted with reckless disregard for human life by selling the family a 1999 Jeep with a gas tank mounted behind the rear axle.

Since then, regulators have fined Fiat Chrysler $175 million in the last year for its slow-moving pace to fix recalls, including Jeeps linked to the fiery crashes.

Additionally, the Jeep issue was the subject of a contentious fight between NHTSA and Fiat Chrysler last summer, when the regulator expressed concerns that the fix was taking too long to occur.

In July 2015, Fiat Chrysler agreed to make trade-in offers to the Jeep owners or pay them to have their hitches installed somewhere other than a dealer, the AP reports.

Despite those initiatives, the AP reports that just 35% of the recalled Jeeps had been repaired by the end of 2015.

[via The Associated Press]