BRUSSELS — A Belgian official’s decision to expel several Sudanese migrants late last year — several of whom say they were tortured when they went back home — has roiled Belgium’s politics, reflecting not only the fraught migration debate in Western Europe but also the divisions that have made the country notoriously difficult to govern.

The official, Theo Francken, is a 39-year-old Flemish nationalist who in 2014 was appointed secretary of state for asylum and migration. He is known for making incendiary comments about migrants; in September, he apologized for using the term “cleaning up” about a police operation in which several undocumented immigrants were arrested. The term was condemned as xenophobic.

Supporters and critics alike have called Mr. Francken “the Flemish Trump.”

Last September, Mr. Francken invited several Sudanese officials to Belgium to review the cases of dozens of Sudanese people who were in the country without authorization. The decision outraged advocates for the migrants, who pointed to Sudan’s abysmal human rights record and the fact that its president, Omar al-Bashir, is wanted by the International Criminal Court for trial on war crimes and genocide charges.

Representatives of the Belgian government were present during most of the interviews, but were not always accompanied by Arabic-language interpreters, raising the possibility that they did not follow all of what was said. Lawyers for the migrants said the Sudanese officials warned that if the migrants applied for asylum in Belgium but were denied and sent home, they would be targeted for abuse.