A United Nations expert says the right of freedom of assembly in the United States is threatened by racial, social and economic inequality.

Maina Kiai, U.N. special rapporteur on the rights to freedom of peaceful assembly and of association, said in a statement issued Thursday that "racism and the exclusion, persecution and marginalization that come with it, affect the enabling environment for the exercise of association and assembly rights."

He said economic inequality, unnecessarily aggressive and militarized policing and disproportionate counter-terrorism measures also contribute to a hostile climate for freedom of assembly.

Kiai issued his statement at the end of 17-day fact finding visit to the U.S. including stops in Washington, New York, Baltimore, Ferguson, Missouri, Cleveland, Phoenix, New Orleans, Baton Rouge, Jackson, Mississippi and Philadelphia.