LONDON: UN special envoy Angelina Jolie says she is "very disheartened" by the US response to the global migration crisis, and fears countries will adopt increasingly isolationist policies instead of acting together to tackle the challenge.

The Oscar-winning Hollywood actress said on Monday that worries about uncontrolled immigration has given a "false air of legitimacy to those who promote politics of fear and separation."

"It has created the risk of a race to the bottom, with countries competing to be the toughest," she said at a migration event sponsored by the BBC in London.

She said nations need to pull together to deal with the world's 60 million displaced people by rebuilding a coordinated and orderly system for dealing with refugees and migrants.

"I have been very, very disheartened by my own country's response to the situation," Jolie said.

The American star also had criticism for US presumptive Republican presidential nominee Donald Trump, who has proposed building a wall to stop Mexican immigrants and called for a temporary ban on Muslims entering the United States.

“It is hard to hear that this is coming from somebody who is pressing to be an American president,” she said in a question and answer session after her speech.

“America is built on people coming together for freedom, especially freedom of religion.”

Conflicts, including the five-year war in Syria, have fuelled a global refugee crisis, with 60 million refugees and displaced people across the world.