A Belgian taekwondo athlete who is the younger brother of a Brussels suicide bomber was barred from a flight to the United States two days before President Donald Trump imposed a travel ban on seven Muslim-majority countries.

Mourad Laachraoui, brother of Najim who took part in the Brussels airport bombings on March 22 last year, was among three people prevented from boarding a flight to the United States on January 25, the Belgian taekwondo association AFBT said.

Also barred was fellow taekwondo athlete Si Mohamed Ketbi and their coach Abdelkhalak Mkadmi as the trio headed to the US Open in Las Vegas, the first major international taekwondo competition of the season, AFBT said.

They had presented their electronic ESTA documents required for citizens of Belgium and other countries travelling to the United States, but an air hostess asked them for visas, which is not necessary, the association said.

The association said it had received overnight an email from the US authorities updating their ESTA and informing them they could not enter the United States, but there was not enough time to notify them.

The association said it was given no explanation for the change and the US embassy in Brussels declined to comment when contacted by AFP.

Trump has run into a storm of criticism since signing an order to ban nationals from seven countries -- Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen -- for 90 days.

Though he is of Moroccan origin, Laachraoui was born in Belgium and has only Belgian nationality, according to officials from his Brussels district of Schaerbeek.

Najim Laachraoui, 24, was one of the two suicide bombers who struck Brussels airport on March 22, while a third attacker blew himself up on a metro train, with the two attacks killing 32 people.

"I was moved and stunned. I didn't want to believe it was him," Mourad said just after the attacks. "But you can't choose your family."