MEXICO CITY — Gunmen who briefly abducted 23 migrants from a Mexican hotel had been planning to demand ransom from their relatives living in the United States, prosecutors said Wednesday.

It was not clear why the armed gang that abducted a total of 39 people from a hotel early Tuesday later released them all, though the prosecutors office in the northern state of San Luis Potosi said it was because the abductors knew they were being sought by authorities.

The office said the migrants among those abducted included Cubans, Haitians and Venezuelans.

Cuban migrants have often been kidnapped for ransom by criminal gangs in Mexico, because they frequently have well-established relatives in the United States who can pay thousands of dollars for their family members’ release. But the practice may now be extending to other nationalities.

Prosecutors said police are investigating the 16 Mexicans also snatched from the hotel in the city of Matehuala where the migrants were staying, to see if any were involved in migrant smuggling. The office said that “the possibility may exist they were informants, or may have been the ones taking them (the migrants) north.”

Gunmen travelling in three vehicles pulled up to the hotel before dawn Tuesday intending to abduct the migrants and force them to hand over telephone numbers of relatives living in the United States, prosecutors said.

The Mexicans were found on a road near a convenience store late Tuesday, and the migrants were found in a nearby hamlet. All are now safe.

Costlier migrant smuggling operations often put up their clients in small hotels as they move them north. Organized crime gangs traditionally charge a tax for each migrant moved through their territory. If that tax is not paid or a rival smuggling group sees an opportunity, such abductions can occur.

Rival gangs also sometimes simply hijack groups of migrants from other traffickers.