A haze resulting from intentional forest fires in Indonesia could have caused 100,000 premature deaths in 2015, new research has concluded. More than 90% of the deaths are believed to be in Indonesia, while the rest are spread out across Malaysia and Singapore.

The research was conducted by US universities Harvard and Columbia, which examined the health effects of pollution that occurs every year because of the burning of forests to clear them for agricultural purposes. In 2015, the haze is believed to have last several months after drifting across South East Asia.

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The study used satellite data and computer modelling to determine the probability of early deaths as a result of the forest fire pollution. However, despite media reports indicating the high number of infant deaths because of the haze, the study only focused on the health of adults.

Researchers analysed the effects of PM2.5, the particulate matter that makes up smog and harms the lungs when inhaled. According to the BBC, the report concluded that the risk from the haze ranged from 26,300 to 174,300 possible early deaths, with 100,300 as the average.

The official number of people who lost their lives during the period of high pollution lies at 19, which includes fire fighters. However, the country's disaster management agency noted that more than 43 million Indonesians had been exposed to the smoke, with half a million suffering from acute respiratory infections.

Last year's forest fires were the worst in Indonesia since 1997. Environmental activists have been calling for the government to take stringent action against the intentional forest fires that occur annually.

"If there is no improvement, deadly smoke will cause worse mortality from year to year," Greenpeace Indonesia forest campaigner Yuyun Indradi said. "Governments and industries must take concrete action to stop the burning of forests."