Three alleged members of the Maute group were arrested Tuesday in Piagapo town, Lanao del Sur.
The suspected members were identified as Jalal Ramal Berongan, alias "Mayor"; Opao Macod Dimacaling; and Ibrahim Alek Undi, alias "Brad Alexander."
They are said to be behind the killing of 3 traders last month carried out allegedly to avenge their relatives who died during the Marawi siege.
Authorities said the 3 admitted to being members of the ISIS-inspired group.
Two firearms were also confiscated from the suspects by Joint Task Group Haribon composed of military and police personnel.
Authorities, meanwhile, warned there are still Maute group members at large.
"We'd like to confirm that there are still some members who are still on the run. There are a few of them left but the government forces are on top of the situation. Although we can't say there is nothing to worry about . . . but we have to help each other especially at the outskirts of Lanao del Sur where they move from time to time," PNP-ARMM regional director Chief Supt. Graciano Mijares said.
The spouse of a Maute group member was also arrested Tuesday in Cotabato City.