THE worst episode of haze here in 16 years has prompted Environment and Water Resources Minister Vivian Balakrishnan to urge commercial pressure against firms causing the haze.

Dr Balakrishnan posted on Facebook on Tuesday that he had spoken to his Indonesian counterpart, Balthasar Kambuaya, to express "deep distress" with the situation: "I suggested Minister Kambuaya name the companies responsible for the fires - (as I am sure consumers will know what to do)."

Choking pollution from forest fires, some started deliberately to clear land for planting, has been an annual affair for years. The worst air quality ever recorded here was during a bout of haze in 1997.

Dr Balakrishnan also urged Indonesia to publish maps of agricultural concessions. "The combination of satellite photos, which are updated daily, and these concession maps would enable us to pinpoint the errant companies," he said.

"I also offered the assistance of the Singapore government - and he said he would revert after his team assesses the situation on the ground."

But on Monday, Indonesian forest ministry official Hadi Daryanto attempted to shift some of the blame onto Malaysia and Singapore, saying their palm oil companies that had invested in Indonesia were also responsible.

Singapore-listed firms like First Resources and Golden Agri Resources have plantations in Sumatra, but both say they have strict policies against burning to clear land.

The three-hour Pollutant Standards Index (PSI), a measure of air quality, stood at 97 at 8pm on Tuesday, a slight improvement from the peak of 155 on Monday night.