Dessy Sagita – Police in Riau say they have arrested a total of 18 people for starting fires in Riau that led to the worst air pollution in the region since 1997.

"We have 18 people in custody," Riau Police spokesman SR.Comr. Agus Rianto told the Jakarta Globe on Friday. "They are all local farmers."

When asked what links the 18 had to palm companies, Agus emphasized that police had not connected the farmers to any concession holders, either domestic or international.

"What we know for now is that they were working individually to clear the land," he said. "We haven't found anything that could connect them to any plantation company."

Agus said that the 18 in custody had viewed slash-and-burn clearing as unproblematic, a practice that had long been carried out in the region.

"Many of them thought there wouldn't be any problem if they put out the fires after they were done," Agus said. "They didn't realize that in peatlands, the fire could happen underground and it could easily spread."

Agus said the number of suspects could grow as the investigation progressed. "Our priority for now is putting out the fires but, rest assured, we will find the perpetrators who have caused this disaster," he said.

The National Disaster Mitigation Agency (BNPB) said that some of the suspects in Rokan Hilir district poured gasoline on land to start fires. "Hundreds of people were also forced to evacuate because of what the suspects have done," BNPB spokesman Sutopo Purwo Nugroho said on Friday.