Keraf said his ministry had ordered the attorney general's office to act on behalf of the government to prosecute the concerned companies, which he did not name.

Many palm oil plantations in Sumatra island use illegal slash and burn methods to clear forestland.

Keraf did not spell out the penalties for those caught, but the state Antara news agency quoted him as saying the government would not resort to "iron-handed" measures, as has been proposed by some environmentalist groups.

Satellite images show dozens of plantation companies have used the burning method to clear forestland, the minister said.

Satellite pictures released Wednesday showed more than 200 fires burning in Sumatra in the second week of July, up from 50 in June, the Meteorological Service Singapore (MSS) said.

Back in 1997, much of the region - including neighbouring Singapore and Malaysia - was blanketed for months by thick smog as a result of forest fires in Sumatra and Borneo, causing extensive health, transport and tourism problems, as well as costing billions of dollars in lost revenue.

Indonesian authorities have vowed to take measures to avoid a repeat of the 1997 smog crisis but claim the financial resources required to do so are being stretched thin by the country's ailing economy.

Teams of Indonesian investigators have already been dispatched to the provinces, and talks on how to deal with the fires will be held next week in Jakarta.

The haze problem is also expected to loom large at the Association of South East Asian Nations (ASEAN) foreign ministers' meeting in Bangkok this coming week.

ASEAN groups Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam. - Sapa-AFP Error: Unable to read footer file.