Jakarta: A satellite observation on Tuesday detected that the number of forest hotspots in Indonesia has risen to 40 from 13 on March 18, with most of them in Sumatra island, an official of the meteorology and geophysics agency said. The Terra and Aqua satellite from NASA detected 37 of the hotspots in Sumatra island, the centre of the country's palm oil industry, and three others in Sulawesi island, Maluku island and Papua, Xinhua news agency quoted the official as saying. Indonesia is home to the world's largest palm oil industry and the traditional annual slash-and-burn methods are the main cause of the forest fires. The country has dispatched aircraft, soldiers, police and firefighters to battle the fires which have been raging since last month, according the national disaster management agency. Last year, the Indonesia government launched the biggest ever battle against massive forest fires across the country that killed 17 people. The fires have brought thick haze to neighbouring countries, triggering serious health problems and huge financial losses.