Migrant families who cross the southern border of the US illegally could be detained indefinitely under a new regulation announced by the Trump administration.

It replaces an agreement that set a limit on how long the government could hold migrant children in custody.

The move was announced by Acting Homeland Security Secretary Kevin McAleenan and is due to come into effect in 60 days.

It is expected to face legal challenge.

Homeland security officials believe that time limits on the detentions of migrant families has driven the surge of Central American families crossing the border into the US this year.

They argue that the new regulation will counter the belief that bringing children into the US is “a passport” to being freed from detention.

“Today, the government has issued a critical rule that will permit the Department of Homeland Security to appropriately hold families together and improve the integrity of the immigration system,” said Mr McAleenan.

“This rule allows the federal government to enforce immigration laws as passed by Congress and ensures that all children in US government custody are treated with dignity, respect, and special concern for their particular vulnerability.”