The Biden administration says four families that were separated at the Mexico border during Donald Trump’s presidency will be reunited in the United States this week.

The families represent what Homeland Security Secretary Alejandro Mayorkas calls “just the beginning” of a broader effort.

Two of the four families include mothers who were separated from their children in late 2017, one Honduran and another Mexican. The parents will return to the U.S. on humanitarian parole while authorities consider longer-term forms of legal status.

The children are already in the U.S.

Exactly how many families will reunite in the United States and in what order is linked to negotiations with the American Civil Liberties Union to settle a lawsuit, but Mayorkas says there are more to come.

“We continue to work tirelessly to reunite many more children with their parents in the weeks and months ahead,” Mayorkas told reporters. “We have a lot of work still to do, but I am proud of the progress we have made and the reunifications that we have helped to achieve this week.”

At least 5,400 children were separated from the their parents at the U.S.-Mexico border since 2017 under the Trump administration's zero-tolerance policy, which criminally prosecuted any undocumented adult who entered the country illegally.