SINGAPORE: Singapore expanded on Friday its probe into companies linked to fires in Indonesia, asking 10 locally-based firms for information about their efforts to contain blazes blamed for toxic haze covering the region.

The city-state has beefed up measures to combat the months-long blazes and had vowed legal action against companies responsible for the fires that have made regional air quality among the world's worst.

Over the past week, Singapore issued notices to 10 foreign-based companies, insisting that they deploy fire fighting teams, stop burning or starting new fires in Indonesia and submit information about their links with associated companies in Indonesia and Singapore.

The information is to be reviewed by Singapore's National Environmental Agency (NEA).