Juul Labs violated US rules against marketing to teens by telling a group of New York high school kids that its wildly popular e-cigarettes were “totally safe,” according to the Food and Drug Administration.

In letters to the vaping giant on Monday, the FDA ordered Juul to stop making unproven claims to children and adults that its vaping devices are safer than cigarettes. It also demanded that Juul turn over documents on its marketing, educational programs and nicotine formula.

“Before marketing tobacco products for reduced risk, companies must demonstrate with scientific evidence that their specific product does in fact pose less risk or is less harmful,” Acting FDA Commissioner Ned Sharpless said in a statement.

“Juul has ignored the law, and very concerningly, has made some of these statements in school to our nation’s youth.”

The FDA highlighted an incident recounted by two New York high school students during a congressional hearing in July. The students said a Juul rep was invited to address the school as part of an assembly on mental health and addiction issues.

During the presentation, the students said the rep told them the company’s product was “totally safe.” The rep also showed students a Juul device and claimed the FDA “was about to come out and it was 99 percent safer than cigarettes.”

Juul says it discontinued its school programs — which were intended to discourage underage use — last September.

In a letter to Juul CEO Kevin Burns, FDA regulators said they also were “troubled” by a number of other points raised at the congressional hearing. The letter cites testimony that Juul’s advertising “saturated social media channels frequented by underage teens,” and “used influencers and discount coupons to attract new customers.”

Last year, Juul closed down its social media sites. And under pressure, it voluntarily removed its fruit and dessert flavors from retail stores.

The FDA also quotes from a “Letter from the CEO” that appeared both on Juul’s website and in an email response to a parent’s complaint about her child being sold Juul products.

The letter touted Juul’s ability “to heat nicotine liquid and deliver smokers the satisfaction that they want without the combustion and the harm associated with it.”

The FDA gave Juul 15 working days to respond in writing about its plans for correcting unproven statements about its e-cigarettes. Failure to do so, the agency said, could lead to financial penalties, product seizures or an injunction.

Juul told The Post that it “will fully cooperate” with the FDA.

FDA warning letters are not legally binding, but regulators can take companies to court if they don’t comply with the government’s requests.

E-cigarettes have been on the U.S. market for more than a decade, but the FDA didn’t gain the authority to regulate them until 2016. E-cigarette makers have until next May to submit their products to the FDA for health reviews.

Most experts, though, agree the aerosol from e-cigarettes is less harmful than cigarette smoke since it doesn’t contain most of the cancer-causing byproducts of burning tobacco. But there is virtually no research on the long-term effects of vaping. E-cigarettes generally heat liquid containing nicotine.