The United Nations said this week that it had “strong indications” that Mexican security forces were involved in the disappearances of nearly two dozen people in Nuevo Laredo, a northern border city.

Twenty-three people have vanished there from February to mid-May, according to the international body’s high commissioner for human rights, Zeid Ra’ad al-Hussein. Human rights groups have documented additional disappearances.

“Many of these people are reported to have been arbitrarily detained and disappeared while going about their daily lives,” Mr. Hussein said in a statement on Wednesday that urged the Mexican government to take action. “It is particularly horrific that at least five of the victims are minors, with three of them as young as 14. These crimes, perpetrated over four months in a single municipality, are outrageous.”