Indonesian police said Friday they were investigating a Malaysian company over forest fires that contributed to choking haze last month, in Southeast Asia's worst pollution crisis in years.

Police said fires were found burning in the palm oil concession of Malaysian company Kuala Lumpur Kepong Berhad held by its Indonesian subsidiary Adei Plantation and Industry.

"On Sunday the national police decided to treat members of Adei as suspects, as we found evidence fires were burning in the companies concession area," said a spokesman for the national police.

The smog crosses the seas from Sumatra every year but hit record levels of pollution last month.

The Malaysian company operates in Indonesian and Malaysia, producing 3.3 million tonnes of palm oil a year, according to its website, and one arm of the company also manufactures palm oil products.

"We have questioned 16 witnesses and if we find the fires were deliberately started, we will further investigate individuals," the spokesman said, adding that starting forest fires was punishable by jail terms.

As fires blazed on parts of Indonesia's Sumatra island for days and angered those in smog-covered Singapore and Malaysia in June, some Indonesian officials lashed back, suggesting companies from those countries were to blame.

The company could not be immediately contacted, but in June it denied allegations of using the traditional slash-and-burn technique in which fires are set ablaze to clear land for new crops.