Malaysian immigration authorities say they have uncovered an Indonesian migrant-smuggling syndicate that moved people from sea crossings to a more elaborate route through Singapore and southern Thailand.

The raid, carried out before dawn on Saturday at two major transport terminals in Kuala Lumpur, led to the arrest of 11 Indonesians, including a suspected transporter, and the seizure of a Mazda CX-5 believed to have been used to move migrants to their next stop.

Immigration director general...