Citing firefighters' reports from Chiang Mai, Chiang Rai, Mae Hong Son and west Kanchanaburi, Suphat said more fires set by villagers had been discovered following an easing in the smog level earlier last week.

"The rise shows that the villagers have not cooperated with the authorities," he said, but did not mention the authorities' failure to enforce fire-control precautions in areas under their jurisdi ction.

Suphat said satellite images showed that there were now 593 so-called "hotspots" in Thailand, 318 of which were in the North. Of these 318, 52 were in Mae Hong Son.

There were a total of 1,243 hotspots in Southeast Asia.

The total number of hotspots has risen rapidly from 387 a few weeks ago, especially in Mae Hong Son, where there were earlier just 27.

Deputy Prime Minister and Social Development and Human Security Minister Paiboon Watanasiritham called an urgent meeting to discuss the smog problem today following an increase in the air pollution index in four key provinces: from 152 to 169 in Mae Hong Son, from 124 to 136 in Chiang Mai, from 100 to 106 in Lampang and from 117 to 121 in Chiang Rai.

An operations centre was set up in Mae Hong Son yesterday to deal with the smog problem, which had affected the province's tourism industry and public health.

Provincial governor Direk Konkleep said 10 THAI flights and nine Nok Air flights between Mae Hong Son and Chiang Mai had been cancelled, and that more than 16,000 people in the province had suffered respiratory problems.

Meanwhile, weeks after the smog problem began, the Royal Forestry Department yesterday issued a number of safety and precautionary measures to cope with wildfires in the provinces.