(CNN) Homeland Security Secretary Kirstjen Nielsen announced Thursday that the United States has told Mexico that individuals entering the US illegally or entering without proper documentation and seek asylum will be sent to Mexico to wait for the duration of their US immigration proceedings.

According to the Department of Homeland Security, individuals entering illegally or without proper documentation "trying to enter the US to claim asylum will no longer be released into our country, where they often disappear before a court can determine their claim's merits."

They will instead "be processed by DHS and given a 'Notice to Appear' for their immigration court hearing."

Asylum seekers from Guatemala, Honduras and El Salvador must wait outside the United States until their immigration proceedings are concluded, according to a Department of Homeland Security official speaking on background during a conference call with reporters Thursday morning.

The "Migrant Protection Protocols," as the DHS official called them, go into effect immediately and will be rolled out in phases along the Southwest Border. Asylum seekers from the Northern Triangle countries will be returned to Mexico, given a notice to appear in court, and will be allowed back into the country for the hearing, the Homeland Security official said. Mexico will continue to provide humanitarian aid to individuals waiting out their legal proceedings near the border, according to the DHS official.

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