Marianne Kearney, Jakarta – Indonesian authorities have identified at least 10 companies responsible for starting fires in the Riau province but are facing problems prosecuting them.

Mr Setyo Winarso, an official of the environmental monitoring agency, Bapadal, said existing laws were difficult to enforce despite the government's readiness to penalise plantation owners.

Despite having the names of 10 companies, government agencies have only been able to investigate one of them, because they had been slowed by the rough terrain and the distances between plantations.

Mr Setyo said existing laws made it extremely difficult to prosecute the company which was found burning a 10 hectare site this week. Under Indonesian law, it has to be proved that the company was responsible for starting the fires. "We have some evidence that the fires were deliberately started but we don't have the person who organised the burning," said Mr Setyo. Mr Setyo said that at the site of palm oil plantation, Pt Adei, the company blamed their contractors for starting the fire.

Despite the passing of a tougher forestry law last year, only one company has been successfully prosecuted out of the dozens of companies that had hotspots detected on their properties. Companies which have been suspected of starting fires often blamed the locals.

Mr Setyo said Bapadal was now hoping to use laws on environmental damage to prosecute all the plantation companies for the high levels of air pollution, rather than investigate each company.

Police spokesman Major Pandiangan said the police were hopeful their investigation into several fires at Pt Adei would uncover evidence that the fires were deliberately started. They have also found two eyewitnesses.

Major Pandiangan said police had yet to investigate another company, Pt Jatim Jaya, which also had several hotspots on its property. Yesterday, the Department of Forestry said it had sent a helicopter to survey the fires.

At another plantation, Pt Musimas plantation, south of Pekanbaru, the haze was so thick that it hampered investigations by officers on board a helicopter, said an official.

Haze levels in Riau are still high, said Mr Setyo, with air pollution index over 100, which is unhealthy. The number of detected hotspots has gone down from Wednesday's high of 564, to only 20 yesterday, probably undetected because of the thick haze.