SINGAPORE/JAKARTA (Reuters) - Air pollution in Singapore rose to the “unhealthy” level on Friday as acrid smoke drifted over the island from fires on Indonesia’s Sumatra island, the National Environment Agency (NEA) said.

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Every dry season, smoke from fires set to clear land for palm oil and pulp and paper plantations in Indonesia clouds the skies over much of the region, raising concern about public health and worrying tourist operators and airlines.

The 24-hour Pollution Standards Index (PSI), which Singapore’s NEA uses as a benchmark, rose as high as 105 in the afternoon. A level above 100 is considered “unhealthy”.

The NEA said it planned a “daily haze advisory” as “a burning smell and slight haze were experienced over many areas” in Singapore.

Indonesia has been criticized by its northern neighbors and green groups for failing to end the annual fires, which were estimated to cost Southeast Asia’s largest economy $16 billion in 2015, and left more than half a million Indonesians suffering from respiratory ailments.

Indonesian President Joko Widodo has increased government efforts to tackle the haze, with police doubling numbers of fire-related arrests this year.

“Forest and land fires in the Riau area are increasing,” Indonesia’s National Disaster Mitigation Agency (BNPB) spokesman Sutopo Nugroho said in a statement on Friday, referring to aerial surveillance of 67 hotspots and smoke from the area drifting eastward over Singapore.

“The smoke billowing from the hotspot locations is quite dense,” Nugroho said, adding that 7,200 personnel and several aircraft had been deployed to stop the Riau fires.

Pollution levels in neighboring Malaysia were normal on Friday.

Singapore has pushed Indonesia for information on companies suspected of causing pollution, some of which are listed on Singapore’s stock exchange.

A forest campaigner for the environmental group Greenpeace Indonesia, Yuyun Indradi, said the government was struggling to enforce laws to prevent the drainage of peatland for plantations and the setting of fires to clear land.

“It has become a challenge for the government to enforce accountability among concession holders, to enforce its directives on blocking canals, and push companies to take part in efforts to restore peatland and prevent fires,” Indradi said.

“Now is the time for the government to answer this challenge. It is in the law.”

Greenpeace said, according to its satellite information, there were 138 fires across Indonesia on Friday.