The Infocomm Development Authority (IDA) said SingTel and two other telecom-linked firms did not fulfil their obligations to customers after the fire at a suburban telephone exchange on October 9. The fine is the highest ever handed to a Singapore telecom firm, according to local media.

Around 270,000 telecom and TV consumers, including residential users, government agencies and businesses, were affected by the disruption.

OpenNet, Singapore's fibre network provider, was separately fined Sg$200,000 while another firm linked to SingTel, CityNet, was fined Sg$300,000.

The IDA's deputy chief executive Leong Keng Thai said the outage was "of a magnitude that is unprecedented, but more importantly, that could have been avoided".

In a statement Tuesday, SingTel apologised for the disruption and said it accepted the fine, adding that the company had enhanced its fire prevention measures and network design.

The company, majority-controlled by Singapore state investment arm Temasek Holdings, wholly owns Australia's Optus and holds substantial stakes in other regional mobile operators including Airtel in India and Globe Telecom in the Philippines.

The SingTel Group has a customer base of over 500 million mobile users across Asia.