Singapore's top ministers have called up 10 of the biggest agribusiness firms based in the republic but with significant plantations in Indonesia, which are being investigated for their links to haze-causing fires.

According to CNA, Singapore Senior Minister K Shanmugam, who is in charge of national security and home affairs, told senior executives of the companies that they are expected to conduct independent probes of their operations.

The investigations will centre on their operations, corporate links and supply chains in Indonesia to determine whether they had contributed to the wildfires, Shanmugam told the corporate officials.

"Haze is caused by fires. Fires are caused by irresponsible business practices. It is not a natural phenomenon,” Shanmugam, who also chairs the Homefront Crisis Ministerial Committee, told the business executives, according to CNA.