WASHINGTON: US President Donald Trump called Monday on NASCAR's only black driver Bubba Wallace to apologize for protests launched over a noose found hanging in his garage stall, which the FBI found not to have been evidence of a hate crime.

The garage door pull-rope fashioned like a noose - widely seen as a symbol of lynchings in the American South - sparked outrage when it was discovered during a period of nationwide protests over police brutality and racism.

Dozens of Wallace's fellow drivers staged a demonstration against bigotry but an FBI probe quickly found that the rope had been hanging in the stall months before the June 23 race at the Talladega Superspeedway in Alabama.

"Has @BubbaWallace apologized to all of those great NASCAR drivers & officials who came to his aid, stood by his side, & were willing to sacrifice everything for him, only to find out that the whole thing was just another HOAX?" Trump said on Twitter.

The noose discovery was made shortly after Wallace had successfully campaigned for a ban on flying the controversial Confederate flag at NASCAR, a popular sport with conservative Americans.

Trump added in his tweet that the ban and the noose controversy had "caused lowest ratings EVER!"