Indonesian national police has investigated firms or individuals involved in forest fire in Riau province of Sumatra that result in haze engulfing Singapore and Malaysia, National Police Chief General Timor Pradopo said in Jakarta Wednesday.

A stern action would be given to company or people proven guilty of burning forest during land clearing to open plantation, said Pradopo.

"We are carrying out an investigation on the forest fire. Whatever the result it would be announced," he said.

Indonesian President Susilo Bambang Yudhoyono on Monday ordered the national police to conduct an investigation following reports that some firms linked with Malaysia were involved in the fire.

Legal actions would be taken against those found guilty, said Yudhoyono.

The police chief said that police were cooperating the country's national disaster management and mitigation agency during the investigation.

The agency has been ordered by the president to take over the effort to put out the fire.

"The investigation has been jointly conducted with the agency," said Pradopo.