Singapore's foreign minister K Shanmugam says his government has asked Indonesia to identify companies that have been involved in slash-and-burn fires in Sumatra that are behind a smoky haze.

The smog caused record levels of air pollution in Singapore and forced hundreds of Malaysian schools to close.

The illegal slash-and-burn fires are used to clear land for palm oil plantations and there have been allegations that some Singapore-based firms may have been involved, though many of them have refuted those claims.

Mr Shanmugam told the BBC that there was conflicting evidence of the involvement of Singapore companies, but said that his government will be "very firm" in its actions against them if any evidence is found.