The U.N. human rights office has "strong indications" that Mexican federal security forces are behind a wave of disappearances in and around the city of Nuevo Laredo, a statement from the U.N. human rights chief said on Wednesday.

Mexican officials did not immediately respond to the U.N. allegations.

The U.N. has documented the disappearance of 21 men and two women in Nuevo Laredo in Tamaulipas State from February until May 16 this year, the statement from U.N. High Commissioner for Human Rights Zeid Ra'ad al-Hussein said.