A US government agency said Tuesday it was investigating fires in Tesla electric vehicles, as the company ordered modifications aimed at reducing what it called a negligible risk.
The move by the National Highway Traffic Safety Administration came after Tesla requested such a probe, saying it wanted to quash any "false perception about the safety of electric cars."
The NHTSA said in a statement it "has opened a formal investigation to determine if a safety defect exists in certain Tesla Model S vehicles."
The investigation "was prompted by recent incidents in Washington State and Tennessee that resulted in battery fires due to undercarriage strikes with roadway debris," according to the statement, emailed to AFP.
Documents posted on the NHTSA website said the agency will "examine the potential risks associated with undercarriage strikes."
Just ahead of the news, Tesla founder Elon Musk said in a blog post that "there is no safer car on the road than the Model S," but said the company would make changes to reduce fire risk.
"We have rolled out an over-the-air update to the air suspension that will result in greater ground clearance at highway speeds," Musk said.
"To be clear, this is about reducing the chances of underbody impact damage, not improving safety. The theoretical probability of a fire injury is already vanishingly small and the actual number to date is zero."
Musk also said he was asking for a "full investigation as soon as possible into the fire incidents" by the US safety agency.
"While we think it is highly unlikely, if something is discovered that would result in a material improvement in occupant fire safety, we will immediately apply that change to new cars and offer it as a free retrofit to all existing cars. "
He added that "the incidence of fires in the Model S is far lower than combustion cars and that there have been no resulting injuries," but said such a probe would reassure customers.
"There is a larger issue at stake: if a false perception about the safety of electric cars is allowed to linger, it will delay the advent of sustainable transport and increase the risk of global climate change, with potentially disastrous consequences worldwide," Musk wrote.
Musk also said that "to reinforce how strongly we feel about the low risk of fire in our cars, we will be amending our warranty policy to cover damage due to a fire, even if due to driver error."
This will be valid "unless a Model S owner actively tries to destroy the car," he said.
Tesla -- whose $75,000 marquee model has been wildly successful, prompting a runup in its share price -- has seen its image hurt by a video of one of the vehicles going up in flames on a street near Seattle, Washington.
Another fire was reported by a Tesla owner in Tennessee.