SINGAPORE - Everyone can play a part in preventing terrorist attacks by staying sharp and reporting any suspicious activities to the authorities immediately, wrote Deputy Prime Minister Teo Chee Hean on his Facebook page on Tuesday.

Yesterday's siege in Sydney showed that "terrorist attacks by individuals can take place even when there is heightened security", added Mr Teo, who is also the Minister for Home Affairs.

This comes three months after the Australian government raised the terror alert to "high". In September, its counter-terrorism officers conducted its biggest security operation and apparently thwarted a plot to conduct a public beheading.

Last night, Prime Minister Lee Hsien Loong expressed his concern on the incident. He wrote on the social networking site that he has sent a message to his Australian counterpart, Mr Tony Abbott, to show support and is confident that Mr Abbott's team is "on top of the situation".

In his post, Mr Teo reminded Singaporeans to remain united and continue working on overcoming terrorism as it is dangerous to all communities in Singapore.

"We should all face it together in a calm and resolute way, and cooperate with the authorities to resolve it appropriately," he said.

Meanwhile, the authorities in Singapore are in touch with those in Australia to find out more details about the incident.

"We are saddened at the loss of life and injuries in the Sydney hostage incident, and our thoughts are with their families and loved ones," Mr Teo said.