Hollywood star Angelina Jolie will step up her work for the world's refugees following her promotion to United Nations special envoy, the UN refugee agency said on Tuesday.

Jolie, a goodwill ambassador since 2001, will take on a "new and expanded" role as special envoy of High Commissioner for Refugees Antonio Guterres, the UNHCR said.

Her work over the last decade, including 40 field visits, "goes significantly beyond the role of a goodwill ambassador," said spokesman Adrian Edwards, and the promotion is intended to recognise this.

The new post will see the Oscar-winning actress perform a more diplomatic role.

"She is expected to focus on large-scale crises resulting in the mass displacement of people, to undertake advocacy and represent UNHCR and Mr Guterres at the diplomatic level, engaging with relevant interlocutors on global displacement issues," said Edwards.