"Inequality is one of the key challenges of our time," said Amina Mohammed, who works in development planning at the United Nations, in WEF's report.
"While it is true that around the world economic growth is picking up pace, deep challenges remain, including poverty, environmental degradation, persistent unemployment, political instability, violence and conflict. These problems, which are reflected in many parts of this report, are often closely related to inequality."
Read MoreRich and poor alike worried about income gap
Last month, Federal Reserve Chair Janet Yellen warned that inequality in the U.S. was near its highest level in a century.
Read MoreYellen: I'm as worried about inequality as anybody
"By some estimates, income and wealth inequality are near their highest levels in the past hundred years, much higher than the average during that time span, and probably higher than for much of American history before then," Yellen said in a speech.