At least 37 people have been killed at an immigration detention center in a Mexican city on the US border after a fire broke out at the facility overnight, the AP news agency cited an official as saying on Tuesday.

The US returns the first migrants to Mexico under a reinstated policy that allows officials to send non-Mexican migrants to that country to await their US immigration court hearings.

The plight of immigrants on the border between Mexico and the United States continues to be a matter of grave concern.

Hundreds of migrants from Central America and the Caribbean trekked across Mexico on Wednesday, the latest in a series of caravans that have sought to reach the US border in recent months

US authorities detained over 1.7 million migrants this fiscal year, new figures show.

The US president is under pressure for ramping up deportations and prosecutions of migrants crossing the southern border.

The Biden administration has announced that it would cancel all construction on the border using diverted military funds, a Pentagon spokesman has said.