The Trump administration says that it has accounted for all immigrant children who have been separated from their families after illegally crossing the U.S.-Mexico border, and is working to reunite them.

A fact sheet released late Saturday by agencies involved in the separations reported that 522 children had been reunited with "adults." Another 16 reunions scheduled for Friday were delayed because of weather affecting travel, but U.S. Customs and Border Patrol (CBP) said those reunions were expected to take place by the end of the weekend.

CBP added that some children were never taken into custody by Health and Human Services (HHS) because their parents' criminal cases were processed too quickly.

HHS previously said that 2,053 minors who were separated at the border were being cared for in its facilities as of last Wednesday, when President Trump signed an executive order aimed at stopping the separations. Officials have said as many as 2,300 children had been separated from the time the policy began until June 9. It was not clear whether any of the 2,000 remaining children were taken into custody after June 9.

According to Immigration and Customs Enforcement (ICE), parents must request that their children be deported with them once they are reunited.

"It should be noted that in the past many parents have elected to be removed without their children," the fact sheet says.

ICE added that it implemented an identification mechanism to ensure ongoing tracking of linked family members throughout the detention and removal process; designated detention locations for separated parents and vowed to ensure communication with children in HHS custody; worked closely with foreign consulates to ensure that travel documents are issued for both the parent and child at time of removal; and coordinated with HHS for the reuniting of the child prior to the parents' departure from the U.S.

As part of the effort, ICE officials have posted notices in all its facilities advising detained parents trying to find or communicate with their children to call a hotline staffed 8 a.m. to 8 p.m. Monday through Friday, or send an email. Attorneys at the border have said they have been frantically trying to locate information about the children on behalf of their clients.

The Associated Press contributed to this report.