A federal judge ruled on Wednesday that the U.S. government violated his court order by attempting to deport migrants to South Sudan, opening another front in a battle between Donald Trump and judges who have imposed checks on the Republican president's hardline immigration policies.

A federal judge ruled late Tuesday that U.S. officials must retain custody and control of migrants apparently removed to South Sudan in case he orders their removals were unlawful.

Lawyers for the immigrants, who aren’t from South Sudan, contend the deportations violate a court order after a previous attempt to send some people to Libya.

South Sudan's President Salva Kiir has reshuffled the senior leadership in the ruling party, according to an official decree, as the country faces fresh fighting between rival armed factions and widespread speculation about Kiir's succession plans.