Image caption Residents of Singapore are wearing masks for protection against the thick haze

The authorities in Singapore 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.

Media playback is unsupported on your device Media caption Hundreds of fires are reported to be spreading smoke from Sumatra

Pollution has reached record levels in Singapore as a result of the smoky haze, affecting millions of residents.

Slash-and-burn clearances Vegetation is cut down and burned to clear land for cultivation

Cheaper than using excavators and bulldozers

Illegal burning of forests to clear land for palm oil plantations is common in Indonesia - particularly in dry season

Indonesia says it is investigating several palm oil companies In pictures: Indonesia fires

However, the smog has now lifted giving residents a glimpse of blue skies on Saturday.

The Pollutant Standards Index (PSI) was 73 at 17:00 local time (09:00 GMT) - below the level at which health advisories are issued.

The PSI peaked at 401 on Friday - the highest in Singapore's history.

Singapore's Prime Minister Lee Hsieng Loong warned on Thursday that the haze could remain for weeks.

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.

The haze is being blamed on illegal burning in Indonesia's Riau province, near the provincial capital Pekanbaru.

Palm-oil firms are accused of using slash-and-burn techniques to clear space for their plantations.

Firefighters in Sumatra are continuing to try to bring the blazes under control.

Environmental group Greenpeace International said its analysis of Nasa data between 11 and 21 June had "revealed hundreds of fire hotspots in palm oil concessions".

"Fires across Sumatra are wreaking havoc for millions of people in the region and destroying the climate," said Bustar Maitar, head of Greenpeace Indonesia's forest campaign.

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.