Four progressive Democratic members of Congress vilified by U.S. President Donald Trump are "fantastic," UN human rights chief Michelle Bachelet said on Thursday.

Trump tweeted over the weekend that the representatives known as "the squad" –  Ilhan Omar of Minnesota, Alexandria Ocasio-Cortez of New York, Rashida Tlaib of Michigan and Ayanna Pressley of Massachusetts – should "go back" where they came from, even though all are U.S. citizens and three are U.S.-born.

Read More:

Trump under fire for attacks on Democratic congresswomen

Trump intensifies attacks on four Democratic congresswomen

"I believe that those four women are fantastic," Bachelet said. "I see bright women who dare to say what they think."

Bachelet was speaking at Geneva's Graduate Institute alongside former South African constitutional judge Albie Sachs, who was giving the inaugural Nelson Mandela human rights lecture on what would have been Mandela's 101st birthday.

Asked if Trump was racist, a question greeted with applause, Bachelet demurred, but Sachs took the microphone and said, "The answer is yes."

Bachelet said she would not use any particular adjective, but said people in a democracy should ensure respect for diversity, for people who think differently and for people of a different color.

"It is not good for leaders, global leaders, (to use) hate speech, saying things that are bad examples or bad models, because it permits and gives license to many others to be xenophobic, to be anti-Islamic, anti-Semitic, anti-everything, anti-foreign," she said.

"That's one of the dangers in the world today."