On Monday, Tesla Motors announced its Model S electric sedan achieved the "best safety rating of any car ever tested."

The National Highway Traffic Safety Administration (NHTSA), which produced the safety rating, isn't happy about Tesla's boasting.

In its announcement, Tesla explained that the Model S earned five-star marks in every category; a rare feat. On top of that, its overall Vehicle Safety Score, provided to manufacturers, gave it a "new combined record of 5.4 stars."

In a statement on its website, the NHTSA issued a rebuke:

NHTSA does not rate vehicles beyond 5 stars and does not rank or order vehicles within the star rating categories. In addition, the agency has guidelines in place for manufacturers and advertising agencies to follow to ensure that accurate and consistent information is conveyed to the public.

The statement doesn't mention Tesla by name, but it's accompanied by a photo of the Model S in crash testing. And it's not buried in a media section of the site, it's on the home page:

A look at the agency's guidelines makes it clear that the NHTSA does not appreciate Tesla's claim that the Model S actually scored 5.4 stars, and that it's the safest car around. Under the heading "Avoid Misleading Technology," they say:

NHTSA strongly discourages the use of potentially misleading words such as "perfect," "safest," "flawless" or "best in class" to describe the star rating received by the vehicle. More acceptable phrases to describe a vehicle receiving a 5-star rating would include phrases such as "highest" or "maximum" safety rating or "top" safety ratings or score.

John Voelcker at Green Car Reports notes "this isn't the first time that Tesla's overreached in its marketing and public relations," and that "its corporate culture seems to include disregarding various rules and practices it doesn't like."

But the fact stands that Tesla earned a safety rating that 99% of cars tested don't reach. And as it's unlikely many consumers check the NHTSA website regularly, it will probably get away with its bold claim.

In an email to Business Insider, a Tesla spokesperson said the company stands by its claim:

We stand by what we wrote in the press release. We believe it to be true based on NHTSA’s numeric Relative Risk Score (RRS) and overall vehicle-safety score (VSS) that ranks cars across its crash-test categories. The VSS score correlates to the overall probability of an occupant being injured in an accident. This data can be found in publicly available government documents online here.

Tesla's vehicle safety score was 0.42, which was lower than any other car listed in public documents.