Officials in Singapore say they are exploring whether to charge two Singapore-based companies in connection with severe smog triggered by forest fires in Indonesia.
The companies own land on the Indonesian island of Sumatra.
Singapore’s foreign minister said he had asked the attorney-general to consider the legal options.
However, he said it was mainly up to Indonesia to take action against the companies.
The firms, Asia Pacific Resources International (April) and Sinar Mas, are headquartered in Singapore but have Indonesian owners.
“The majority of hotspots in Riau (province) are inside April and Sinar Mas concessions,” Indonesian presidential aide Kuntoro Mangkusubroto told Reuters news agency.
Asia Pacific Resources International has issued a statement to the BBC denying the allegations.
Pollution has reached record levels in Singapore as a result of the smoky haze, affecting millions of residents.
Correspondents say the fires come from illegal burning in Sumatra that takes place in the dry season to clear space for palm oil plantations.
Foreign Minister K Shanmugam also said he would bring up the issue at a meeting of South-East Asian Nations (Asean) taking place in Brunei next week, and he has not ruled out appealing to other international bodies.
A senior official in the Indonesian president’s office said fires had been spotted on land owned by 32 companies in the region, some of them based in Malaysia and Singapore.
Schools in parts of Malaysia and Indonesia have closed temporarily.
Singapore’s Prime Minister Lee Hsieng Loong warned on Thursday that the haze could remain for weeks.
The Pollutant Standards Index (PSI) hit 401 at 12:00 on Friday (04:00 GMT) – the highest in Singapore’s history.
On Saturday at 10:00 local time (02:00 GMT) the PSI was at 326 – a level still considered hazardous.