Zeid, who rarely communicates on Twitter, said in a tweet that "discrimination on nationality alone is forbidden under human rights law", adding that "the US ban is also mean-spirited and wastes resources needed for proper counter-terrorism."
Trump Friday signed an executive order suspending the arrival of all refugees for at least 120 days, Syrian refugees indefinitely -- and barring citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for 90 days.
The measures introduced a week after his inauguration were fiercely criticized over the weekend, although UN reactions were largely tepid.
The UN bodies most directly engaged with migration -- the UN refugee agency and the International Organization for Migration (IOM) -- issued a statement Saturday which made no mention of the executive order and stopped far short of condemning it.
Instead, the agencies urged the US to "continue its strong leadership role and long tradition of protecting those who are fleeing conflict and persecution."
They also vowed "to engage actively and constructively with the US Government... to protect those who need it most".