Formula 1's governing body made clear in Mexico that it wanted a public apology from Max Verstappen.
A week ago, the Dutch driver was believed to have been referring to Garry Connelly when he said that a steward who repeatedly penalises him was a "mongol" and "idiot".
Verstappen withdrew the 'mongol' insult, but amid reports that the FIA wanted an apology, he stood by the other criticism.
"When you are unjustly taken off the podium after a race, it seems normal to me that you are angry," Verstappen is quoted as saying by newspaper Algemeen Daghblad.
"Unfortunately I cannot change the word that I used."
F1 race director Charlie Whiting, however, hit back at the suggestion that one steward was responsible for the decision, saying all four officials in Austin voted for the penalty.
"Until now Max has not apologised. But it would be good if he did," he added.
Verstappen later wrote on Instagram: "I once again apologise for the language that I used following the US grand prix.
"I know that the words I used were inappropriate and they were not directed at any one person."
Another US GP steward, former F1 driver Mika Salo, revealed this week that he received death threats from some of Verstappen's fans.
