The haze that affected Singapore from Friday to Sunday was caused by forest fires burning in Rokan Hilir in Sumatra's Riau province, Indonesia's National Disaster Management Agency (BNPB) said yesterday.

Dr Sutopo Purwo Nugroho, who heads the BNPB's data and information division, said the smoke was carried to Singapore by winds unleashed by Typhoon Lionrock in the Philippines.

The tropical cyclone has since left the Philippines and was moving towards Japan yesterday.

"The cyclone not only sucked in the haze but also the moisture in Riau, making (the air) drier," said Dr Sutopo during a briefing at the BNPB headquarters in Jakarta.

Satellites detected 162 "fire alerts" in the Rokan Hilir regency between Friday and Sunday. The fire alerts accounted for almost half of all the 338 fires detected across Sumatra and Kalimantan over the same three days.

The fires were exacerbated by a combination of dry conditions, sporadic rains and the illegal use of fire for land clearing.

"Eradicating such acts is impossible, although minimising it is possible," said Dr Sutopo, who was referring to the use of the outlawed slash-and-burn method of land clearing.

He added that the focus of firefighting efforts over the next few days will be in Rokan Hilir, but that after a bout of rainfall - which was partly the result of cloud-seeding operations - conditions are expected to improve.

While the hazy conditions in Singapore cleared up by yesterday, heavy haze hit most parts of Kuala Lumpur, with air pollutant readings in the Malaysian capital reaching near "unhealthy" levels, Xinhua news agency reported.

The 88-storey Petronas Towers were barely visible in the thick haze, which reached even the office of Malaysian Prime Minister Najib Razak, prompting him to tweet: "The haze is back in some areas, so please take healthcare measures, especially the old and the young."

Francis Chan and Wahyudi Soeriaatmadja