A satellite observation on Tuesday detected that the number of forest hotspots in Indonesia had reached 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 center of the country's palm oil industry, and three others in Sulawesi Island, Maluku Island and Papua, the official told Xinhua by phone.

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 there 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 neighboring countries, triggering serious health problems and huge financial losses.