KUALA LUMPUR, Malaysia — Heavy haze forced Malaysian authorities to shut schools Tuesday in three states and two key cities as aircraft prepared to begin cloud-seeding operations to induce rain to help clear the air.

Indonesia intensified efforts to extinguish the forest fires that cause the haze, which blanketed parts of the archipelago and neighboring countries. President Joko “Jokowi” Widodo ordered agencies to use all means, including deploying more troops, to overcome the haze.

The thick, dirty white haze is an annual phenomenon mostly caused by fires illegally set in Indonesia to clear land for farming.

A plane equipped with chemicals that will help clouds produce rain was due to fly over Kuala Lumpur and surrounding areas, said Maznorizan Mohamad, a meteorological department senior official. A second aircraft was scheduled to fly over Kuching in Sarawak state on Borneo island.

She said the cloud-seeding is planned for three days but will depend on cloud availability and weather conditions. The inter-monsoon season is expected to start in late September, bringing more rain over peninsular Malaysia to clear up the haze.

“It will bring temporary relief but whatever it is, we have to address the source of the problem,” she said.

Indonesian President Jokowi said he ordered law enforcement agencies to take “stern actions” against those responsible for the fires. “The stern actions include revocation of their forest concessions,” the presidential office quoted him as saying.

Indonesia’s National Disaster Mitigation Agency dispatched 1,250 troops to the most stricken province of Riau on Tuesday.

Indonesian police said they are investigating 131 cases of land and forest burning in several provinces.