Filippo Grandi of Italy has taken the helm at the United Nations' refugee agency, saying it faces "extraordinarily difficult" times and urging renewed efforts to tackle the problems that have caused millions worldwide to flee.

The 58-year-old Grandi previously headed the agency that assists Palestinian refugees, the U.N. Relief and Works Agency.

Grandi, who also worked in several locations for the U.N. High Commissioner for Refugees, succeeds Antonio Guterres as its head. Guterres stepped down after a decade in charge.

Grandi arrived at UNHCR's Geneva headquarters Monday. He said in a statement the agency "is navigating extraordinarily difficult waters."

Grandi says "the combination of multiple conflicts and resulting mass displacement, fresh challenges to asylum, the funding gap between humanitarian needs and resources, and growing xenophobia is very dangerous."