A high performance version of the new Lexus LS has been spotted doing hot weather testing in southern Europe.

With the Lexus LS F-Sport already unveiled at this year's New York motor show, we're pretty certain this car is a prototype for the first ever LS F.

Although the prototype uses primarily stock parts, this LS does have an unpainted front bumper, and covered up Lexus badges, as well as a new rear spoiler and a taped over badge on the trailing edge of the rear door.

The car also features a large cut out in the lower portion of the spindle grille, indicating there's a more powerful engine lurking beneath the bonnet.

Although the prototype uses the hybrid LS500h's rear bumper and has no visible exhaust outlets, the spy photographer noted the car was much louder than a regular Lexus.

Rumours indicate the LS F may feature a twin-turbo V8 rather the naturally-aspirated 5.0-litre V8 doing service in the RC F and GS F, as well as the new LC500 coupe.

In order for the new LS F to be seen as a true competitor to the Germany's performance sedans, the LS F will need to be in the same power and torque ballpark.

The latest Mercedes-AMG S63 features a 4.0-litre twin-turbo V8 with 450kW of power and 850Nm of torque. That's a big step up from the 310kW/600Nm offered by the LS500's 3.5-litre twin-turbo V6.

Timing for the reveal and launch of the Lexus LS F is not known, but the car could debut as early as the Frankfurt motor show in September.

The Lexus LS500 and LS500h are set to make their way into Australian showrooms during the first quarter of 2018.