Mercedes team principal Toto Wolff has described Red Bull's contentious ride-height device as "outrageous" and demanded the FIA investigate it further.

The build-up to Sunday's United States Grand Prix in Austin – won by Ferrari's Charles Leclerc as Red Bull's Max Verstappen finished third – was dominated by speculation about a device found on the RB20 car.

Rival teams have suggested the device could be used to advantageously alter the car's ride height when teams are in restricted 'parc ferme' conditions.

Under the 'parc ferme' regulations, teams are prohibited from making adjustments to their setups between the end of qualifying and the start of a race. 

Constructors' championship contenders McLaren are among the teams to have questioned the device, though Red Bull team principal Christian Horner insisted it was not accessible to use when the car was fully assembled.

Mercedes chief Wolff – a long-time rival of Horner's – has now entered the debate, calling on the FIA to take action.

"My view is from a distance, what I've seen and what I've heard, it's outrageous," Wolff said. 

FIA officials were seen observing a demonstration of how the device operates in advance of Sunday's race, but Wolff is not sure those checks were adequate.  

"I really liked that, when they put this broom in the car to demonstrate the only way that the height could get changed," Wolff said.

"I wonder how long it took them to make this, and to stick it in there. I didn't know that in Formula One that we were using such devices!

"It's not good enough to say, 'that's it, we promise we're not going to do it again'.

"I cannot speak for the FIA at all. Obviously, that's something that's not been spotted for a long time. I think the leadership of the FIA is going to look at that and say, 'what are we doing with this?'"