Malaysian Prime Minister Najib Razak has called on Indonesia to take action against people setting fires that have caused choking smoke to drift across the region, with the sky over southern Thailand the latest to be clouded by the pollution. Indonesia has come under pressure in the past few weeks to contain the annual haze crisis, which is caused by slash-and-burn agriculture on Sumatra island and its part of Borneo island. Companies seeking to clear land for palm oil and pulp wood plantations have been accused of encouraging the fires that often smoulder for weeks in underground peat deposits. The problem has been exacerbated this year by the El Nino weather phenomenon which has brought unusually dry conditions. "If this is done by people or by farming companies, Indonesia needs to take decisive action against the perpetrators," Najib said on Twitter late on Sunday. Schools in Malaysia and Singapore have closed when the smoke has been heavy, sports events have been cancelled and tourism operators are fretting. Health authorities across the region warn people to avoid exercise on bad days. Indonesia routinely brushes off complaints while at the same time vowing, year after year, to stop the burning. Indonesian Vice President Jusuf Kalla was recently reported as chiding neighbours to be grateful for the 11 months of clean air his country’s forests provide outside the haze season. Indonesia has also repeatedly declined offers of help to tackle the fires from its neighbours. Indonesia’s national disaster management agency said last week it was hoping for rain to help douse the fires by early November, when the northeast monsoon usually starts. Thai environment officials said the level of pollution from Indonesia has risen sharply in the south of the country, near the Malaysian border, and health authorities were opening hotlines to provide advice and issuing face masks. Indonesia says more than 200 companies, most of them from Southeast Asia, are being investigated on suspicion of causing fires. Police said ne company from Australia, palm oil plantation operator PT Kayung Agro Lestari, and one from China were among them. Police did not identify the Chinese company.