"We hope that the measures concerning the suspension of refugee flows are temporary as refugee protection needs have never been greater," said UN spokesman Stephane Dujarric.
"The US resettlement programme is one of the most important ones in the world."
Trump yesterday signed an executive order suspending the US refugee resettlement program for 120 days.
In addition, all visa applications from seven Muslim countries -- Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen - were put on hold for at least 90 days.
Yesterday, UN Secretary-General Antonio Guterres told a Holocaust commemoration that discrimination against migrants and refugees along with the stereotyping of Muslims were opening the door to more extreme hatred.
"A 'new normal' of public discourse is taking hold, in which prejudice is given a free pass and the door is opened to even more extreme hatred," Guterres told the General Assembly.